There is an interesting article here: Small Cog in a Big Wheel: Porpoise Ammunition Sledges Re. Porpoise Ammunition Sledges And there's a ref. in the SRY war dairy: "23rd May 1944 Major Christopherson visited a demonstration of “Porpoise” at the Fawley area. During the evening some “porpoises” arrived in the Hursely area." From the article at: Small Cog in a Big Wheel: Porpoise Ammunition Sledges "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." David Fletcher's book: "Swimming Shermans: Sherman DD amphibious tank of World War II" Has on p42 “It may seem to be tempting providence to launch a DD tank with a trailer, especially after the experience with the Porpoise.” Swimming Shermans There's a further bit in the article at: Small Cog in a Big Wheel: Porpoise Ammunition Sledges With "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." Which seems to tally with the SRY's Major Christopherson visiting a demonstration of “Porpoise” at the Fawley area, on 23rd May 1944 a few weeks before D-Day. And if the SRY were towing porpoises themselves they might have done so perhaps with their one non-DD Sherman squadron perhaps. It seems possible from the David Fletcher quote above in "Swimming Shermans: Sherman DD amphibious tank of World War II" e.g. “It may seem to be tempting providence to launch a DD tank with a trailer, especially after the experience with the Porpoise.” That there's a further reference to negative experiences with the towed Porpoise with the DD tanks. I did look to see if there was any "evidence that Sherman DD units were actually issued with them." e.g. : Sherman DD tank near porpoise - Google Search But it's still a grey area (for me), at least as far as I can see at the mo. All the best, Rm.