Friday, 29 March 2013

Porpoise Ammunition Sledges

This article isn’t meant to be a full technical description of the Porpoise and it’s construction. My reason for starting it was a realisation that whilst the existence of the Porpoise is well known to most modellers with an interest in D-Day, very little has been written about how they were actually employed by the units involved. Whilst researching the role of 27th Armoured Brigade and the Sword Beach landings, I started to come across references to the use of Porpoises by a number of regiments and it seemed to me that further investigation would prove useful.

One of the many concerns of the Overlord planners was the provision of sufficient ammunition for the tanks involved in the initial assaults. Whilst provision had been made for the landing of ammunition lorries as early as H+15 minutes, there were still worries about the amount of ammunition available. A novel solution to this problem was proposed and this became the Porpoise sledge. This was a long, shallow metal 'box' divided into two compartments, each sealed with a watertight lid. The towing vehicle was a tank or self-propelled gun. When fully loaded, the sledge was dragged along the seabed but if only partially filled, it would float behind the tank. Once on the beach, the sledge was dragged behind the tank to a collection point. This provided an instant ammunition reserve for units operating close to the beaches.

Although designed to float when partially loaded, it was almost certainly not used in this role. Trials were carried out using a Valentine DD and this seems to have been successful. The Valentine DD's single propeller meant that the towing eyes on the rear of the tank were available to tow the Porpoise. When it came to the Sherman DD, the twin propellers were located in such a way that the normal towing eyes would be masked by the props – making towing by this method impossible. Instead, new towing lugs were fitted under the lip of the skirt. However, despite this there is no evidence that Sherman DD units were actually issued with them. Whilst it was quite feasible for a wading tank to tow a floating Porpoise ashore, it would make little sense. Why half-load a Porpoise so that it could float, when you can fully load it and drag it ashore behind a wading tank? The maximum 'floating' weight was 1280 lbs – anything more and the sledge was dragged along the seabed to the shore.

The Porpoise sledge was produced in two sizes, although it is unlikely that the narrower version was used operationally. The Porpoise No. 1 Mark 1 was designed to fit between the tracks of smaller tanks such as the Matilda and Valentine. The Porpoise No. 2 Mark 1 was wider and would sit comfortably between the tracks of the likes of Churchills, Shermans and Cromwells. Although it was perfectly feasible for the Porpoise to be towed by trucks and other vehicles, there was no practical advantage to this. The whole purpose was to stow the sledge underneath vehicles on the landing craft to maximise load space - the wheelbase of most wheeled vehicles was too narrow to permit this. However, some armoured regiments had other ideas as we shall see shortly…

The description and notes below refer exclusively to the wider No.2 Mk 1 Porpoise.

The No. 2 sledge was a pressed steel box, 13' 6'' long, 4' 6'' wide and 1' deep. It was designed to carry a variety of ammunition, ranging from rifle calibre ammunition to 105mm howitzer shells - depending on the vehicle it was intended to support. Two removable hatches in the top of the sledge allowed access to the ammunition lockers. These lockers were filled with a series of metal cages – the standard fit being 24 cages. When configured to carry 17 pdr ammunition the normal cages were replaced with 10 special cages, each carrying three shells. A series of wooden packing strips to held the cages in place.

The Porpoise was attached to the towing vehicle via a pair of telescoping towbars. These could extend from 6' 11'' when fully stowed, to 12' 6'' when fully extended. The vehicle attachment points were fitted with explosive bolts, so that the sledge could be jettisoned if necessary. When towed off a landing craft, the maximum recommended ramp angle was 25 degrees. If the ramp was steeper, there was a likelihood that the towing bars would become distorted. However, the official pamphlet points out that this would not necessarily make them unusable in the short term.

Although the idea was to load the Porpoise before it was embarked, practical tests showed that it was much better to tow the sledge aboard empty and then load it. The primary reason for this was that the sledge needed to be manhandled into place and an empty sledge was far easier to move about. Once aboard, the Porpoise was then loaded with the required ammunition. Each Porpoise was issued with a 15 foot length of chain, to be used when towing the sledge aboard a landing craft. The chain was linked to the back of the Porpoise and attached to the front of the towing tank. The tank reversed onto the landing craft, dragging the Porpoise into the vehicle well.

There were two methods recommended - differing only in the number of vehicles involved. The first option was that each tank would tow a Porpoise aboard. The Porpoise would be disconnected from the tank, positioned on the deck by hand, loaded, sealed and then the tank was backed over it. The second option was to use one tank to tow all the sledges aboard in turn. In both cases, the ammunition was brought aboard the landing craft on RASC trucks and stacked in 'loads', each one placed along the edges of the tank deck adjacent to where each Porpoise would be located. Although photos of Porpoises being loaded onto landing craft before D-Day exist, it is unclear whether the Porpoises are empty. It may be that the loading notes came as a result of the D-Day experience (the pamphlet initially used as a reference was published in October 1944).

The original idea was to stow each Porpoise under it's own towing vehicle. However, experience soon demonstrated that it took too long to hitch up the sledge and disembark the tanks. Each vehicle would have to move forward, wait until its Porpoise had been attached and then disembark. Instead, the Porpoise was linked to the tank directly ahead of it. This allowed almost all the sledges to be linked up before the landings commenced. The rearmost tanks in the landing craft clearly didn't have this advantage, so their Porpoises were placed adjacent to the vehicles and were attached to the tanks before they disembarked.




So much for the theory - how were they really used?
The Porpoise was widely used on D-Day, but again, little photographic evidence remains. Most assault units on the British/Canadian beaches employed the Porpoise but it is seldom mentioned in any detail in their own records. The Royal Engineer Assault Regiments towed them behind Churchill AVREs. The Royal Marine Armoured Support Group (RMASG) hitched them up to their Centaurs and the armoured assault brigades (of which the DD regiments were part) used them too. What seems clear from some records however is that many crews had not actually towed them prior to D-Day. This suggests that as with many other types of specialised equipment designed for D-Day, sufficient quantities were only available at the last minute.

Leaving nothing to chance, stowage diagrams were issued for each type of landing craft used for the D-Day landings. The three types in question were the LCT Mk 3, 4 and 5, It does not appear that Porpoises were towed by vehicles being carried by larger craft such as LSTs (Landing Ship Tank)*. The smallest type, the LCT Mk 3, could carry up to six large armoured vehicles (tanks or SP guns) and a similar number of Porpoises. If all six vehicles were towing Porpoises, they were stored underneath the vehicle immediately behind the towing vehicle. The exception was the rearmost vehicle, which clearly had no room behind it. In this situation, the porpoise would be stowed beside the vehicle, ready to be hitched up as soon as space available for the vehicle to pull forward as the others disembarked. The larger LCT Mk 4 could carry up to nine large AFVs with Porpoises. Once again, the sledges for the rearmost tanks were stowed between the two rows of vehicles rather than under them. The American-built LCT Mk 5 was different again and in this case, all the porpoises could be linked up to their towing vehicles before disembarkation.

* A possible exception to this might be A Squadron of the East Riding Yeomanry. ERY were part of the reserve element for Sword Beach and were not expected to land before the early afternoon. They were originally meant to travel across the Channel in LCTs, and indeed for Exercise Fabius IV on 4-5 May 1944 landed in this fashion. However, due to a shortage of LCTs (possibly related to the decision to assign more LCTs to some earlier waves in order to lighten each craft's load), they were instead loaded into an LST. On arrival off Sword Beach on the afternoon of 6th June, they transferred to Rhino Ferries for the last stage of the journey to the French Coast. The hair-raising description of this transfer from ship to ferry in the choppy waters off the coast is bad enough, but trying it with a Porpoise in tow would have been an absolute nightmare. It's unlikely, but not impossible that Porpoises were embarked with this Squadron.

In practice, the number of Porpoises carried in any LCT (if they were carried at all) seems to have averaged about five. It was therefore possible to load each LCT in a way that ensured all the Porpoises were hitched up before disembarkation. On LCT 610 (chalk no. 212), carrying elements of 13/18 Hussars, three Porpoises were embarked. Whilst there were six tanks on board, two belonged to the regimental HQ and one vehicle was the C Squadron ARV. The other three tanks all belonged to C Squadron and all towed Porpoises ashore including ‘Carole’ (a Sherman Vc Firefly, turret no. 71), subject of the Dragon 1/35 and 1/72 scale kits.

Another source of Porpoise information is the landing tables for D-Day. These comprehensive listings are held at the National Archives in London and lay out the individual loads carried by each landing craft and the units to which the vehicles and troops belonged. Whilst they should not be relied upon in isolation, having been issued originally on 19th March 1944 and modified here and there at a late stage, they remain largely accurate. The tables list the number of Porpoises carried in each craft. The only 'first tide' listing I have found are those for 3rd British Infantry Division (Sword Beach). Listings also exist for Juno and Sword Beaches, but they only cover later landing sequences.

As mentioned earlier, I came across a number of references to the use of Porpoises whilst researching the activities of 27th Armoured Brigade and this prompted me to look into the subject more widely. Further searching turned up more references to Porpoises as used by other units, but not in the same degree of detail. The following notes concentrate on 27th Armoured Brigade simply because it is the area in which I have undertaken most research. Other information is also listed where I have been able to find it.

27th Armoured Brigade
The Regimental and Brigade War Diaries, along with personal memoirs from the regiments, make comments about the employment of Porpoises. A range of photographs also exist of C Squadron, 13/18 Hussars as they prepared for the invasion. Many show the Porpoise towing arms stowed across the front of the tank in addition to the spare track, roadwheels and return rollers that virtually all tanks within 27th Armoured Brigade carried. There are also photos of C Squadron loading their tanks onto landing craft, late on 3rd June 1944. These demonstrate the approved method of loading the porpoises. As each tank backed into the LCT, it dragged a Porpoise backwards using a chain issued for the task.

The 27th Armoured Brigade Operations Order No. 1 for Operation Overlord lays down a specific procedure for the employment of Porpoises. The brigade included three armoured regiments, each operating Sherman Tanks. 13/18 Hussars would operate two squadrons of Sherman V DD tanks and one of Sherman III wading tanks (with four Sherman Vc Fireflies) for the initial assault. The Staffordshire Yeomanry would operate as a 'wading' regiment and come ashore around three hours later, whilst the East Riding Yeomanry would also operate wading tanks and come ashore in the early afternoon. The latter regiments operated Sherman IIIs, with Sherman Vc Fireflies.

The 15 Porpoises belonging to 13/18 Hussars were towed ashore by tanks from C Squadron, who landed at around H+45 minutes. Their purpose was to provide replenishment for the DD tanks that had arrived at H-Hour and might now be short of ammunition. Once ashore, the porpoises were to be dumped in an area above the high water mark that had previously been cleared by flail tanks. Specific instructions were given about not leaving the porpoises below this level because of the danger they would pose to other vehicles when they were covered by the rising tide - particularly 'B' vehicles (trucks and other softskins).

Where possible, the tanks would return to the drop-off point to re-arm. Given that this might not prove possible, the Ops Order instructs each regiment to assign two half-tracks to ammunition re-supply duties. The crews of the half-tracks would open the porpoises at the drop-off point and load as much ammunition as possible into the vehicles. They were also instructed to tow unopened Porpoises to wherever the tanks were situated, should this prove necessary. Once the ammunition had distributed, the half-tracks would report to the Regimental Aid Post (RAP) and come under the command of the Medical Officer. If required, the half-tracks would report to the RAP earlier.

The same procedure was laid down for Staffordshire Yeomanry, landing at around 1040 (H+195) and East Riding Yeomanry who were due to land at around 1330 (H+360). Each regiment had its own drop-off point, normally the initial rally point and de-waterproofing area.

The concept of using half-tracks to tow fully loaded Porpoises had been tested out whilst the Brigade was based in Scotland in March 1944. A vehicle from 13/18 Hussars was used to try the idea out and whilst the regimental War Diary makes no mention of the outcome of these tests, it was clearly considered a success. Within days of the trials, the method had been incorporated into the planning for the final landing exercises before Overlord. Although included in the planning, other accounts indicate that for most tank crews, their first experience of towing Porpoises was at the beginning of June 1944, as they moved from their camps towards the embarkation points on the coast. The War Diary of the 13/18 Hussars comments that this last minute introduction to the Porpoise caused delays on the road march, as each crew got used to the towing procedure.

Once ashore, C Squadron 13/18 Hussars found the planned drop-off point for the Porpoises was unsuitable.
Those that survived the journey across the beach were towed further inland to another rally point before being left. Of the 15 Porpoises issued to 13/18 Hussars, only five survived the trip across the beach. The other ten were left on the beaches, mostly as a result of being run over by other tanks and ripped off the backs of the towing vehicles. The C Squadron Diary relates that in most cases, it was the towing arms that gave way, leaving the Porpoise itself stranded in the middle of the beach. Given the well-documented congestion on the beaches and the delays in clearing the beach exits, it perhaps surprising that any Porpoises survived the experience. Of the remaining five sledges, at least one was run over on the beach but remained attached to its tank, albeit at a somewhat drunken angle. This belonged to Lt Eric Smith, Troop Leader of No. 4 Troop. He towed his Porpoise inland, with the sledge following slightly to one side of the tank. As the tank rounded a corner, the wayward Porpoise caught three soldiers unawares and knocked them off their feet. Thankfully no injuries were incurred and having checked on the state of the soldiers, Lt Smith proceeded on his way.

Arriving some three hours later, the Staffordshire Yeomanry also had problems getting off the beach. The rising tide had reduced the beach to little more than a thirty foot stretch of sand. They were stuck in a traffic jam for nearly an hour, before they were able to move off the beach through their designated exit. Given these delays, Lt-Col Eadie, their CO, decided to bypass the initial rendezvous point and move directly inland to a crossroads near Hermanville before regrouping. Although no detailed reference is made to their use of Porpoises, their war diary does note that they dumped their porpoises in this assembly area.

Other references to Porpoise use.
These are in no way meant to be a comprehensive listing of Porpoise references. They are purely those that I have come across in my other research.

The Centaurs of 5th Independent Battery RMASG (Royal Marine Armoured Support Group) apparently towed two Porpoises. After waiting for some time near the waterline, the tanks moved up the beach towards the first ‘lateral’ (the first road along the shore, virtually on the beach). Medical teams on the beach used this as an opportunity to move casualties up the beach by loading them onto the Porpoises.

76th Field Regiment (RA) towed Porpoises ashore on Sword Beach behind their M7 Priests. There is little comment about their use, but Norman Scarfe in 'Assault Division' (his history of 3rd Infantry Division in NW Europe), includes a comment that suggests the Porpoises were considered more trouble than they were worth. As a young subaltern in 76th Field Regt at the time, his comments probably come from the heart.

13th Canadian Field Artillery, landing M7 Priests on Juno Beach, had other concerns. The friction caused by prolonged towing of the sledges, particularly over hard-surfaced roads, caused a build-up of heat in the ammunition compartments. There were fears that this heat build-up could cause an explosion. Extended towing over hard surfaces also led to a rapid deterioration in the bottom plate of the sledge. By the time the regiment's Porpoises had reached the drop-off point some way inland from the beach, several of them were worn through on the undersides.

86 Field Regt RA (Hertfordshire Yeomanry), the only regiment to land Sexton SP Guns on D-Day (Juno Beach), found that their Porpoises caused less trouble than expected. The C Troop diary records:

"The Porpoises - those misbegotten children of the "War House" proved to be quite amenable to a wet landing and all were landed without any trouble. Perhaps this was as a result of the language used on them previously....".

The first Troops ashore were A, C and E Troops, landing at around H+60, or roughly 30 minutes ahead of schedule. B, D and F Troops landed at around 1000. The vehicles were delayed on the beaches before moving inland. Their diary records that they reached the Mont Fleury Battery and dumped their Porpoises at this point. However, there is also evidence that some of the more enterprising gun sergeants used the delay in getting off the beaches to unload the Porpoises and cram the spare ammunition into any available nooks and crannies in the vehicles, rather than tow them any further inland. This may account for the presence of some abandoned and apparently empty Porpoises in one or two photographs of the Juno beach areas.

The Sherbrooke Fusiliers, landing on Nan White Beach (Juno) at around 1215, record that their Porpoises were used as impromptu infantry transports, carrying infantry of the North Nova Scotia Highlanders to the main assembly area codenamed 'Elder'. Long delays due to congestion on the roads meant that they didn't reach Elder until around 1800.

My thanks to Neil Wharton, Nick Perry, the Tank Museum Library and the National Archives in London for information, assistance and ideas in equal measure.

Porpoise Ammunition Loads
(Ammunition was loaded into 24 baskets within the Porpoise – except for 17 pdr ammunition). The steel baskets were of a standard size, so in theory, each Porpoise could carry a mixed load of ammunition (in particular a mix of 75mm and machine gun ammunition for the tanks). However, the implication of various records would suggest that only one type of ammunition was carried in each Porpoise – with the ammunition type being indicated on loading stencils on the upper deck of the sledge.


Calibre Per Basket Floating* Full Load
7.92mm Besa 4 boxes 54 boxes 96 boxes
.30 cal 4 boxes 64 boxes 96 boxes
.50 cal 2 boxes 44 boxes 96 boxes
6 pdr 4 rounds 70 rounds 96 rounds
75mm 4 rounds 50 rounds 96 rounds
25 pdr 2 rounds ?? ??
95mm** ?? 38 rounds 48 rounds
105mm** ?? ?? ??
17 pdr# 3 rounds ?? 30 rounds

*The maximum load for floating Porpoises could not exceed 1280 lbs, so the basket loads were reduced accordingly.

** Contemporary records indicate that this ammunition type was carried in Porpoises, but no official stowage details have been found.

# 17 Pdr ammunition was significantly larger than other types and was carried in ten specially constructed cages in the Porpoise

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