Porpoise class Minelayer Submarine
Name Pennant Builder Completed Fate
Porpoise 14M Vickers 11/3/33 Bombed by Japanese off Penang, 19/1/45
Grampus 56M Chatham RDY 10/3/37 Depth-charged by Italian motor boats Circe and Clio off of Sryacuse, 16/6/40
Narwhal 45M Vickers 28/2/36 Bombed by Germany in North Sea, 23/7/40
Rorqual 74M Vickers 10/2/37 Scrapped 1946
Cachalot 83M Scotts 15/8/38 Rammed by Italian motor boat Generale Achille Papa off Benghazi, 30/7/40
Seal 37M Chatham RDY 24/5/39 Mined & captured by Germany, 5/5/40, to Germany as UB 1940, scuttled 3/5/45
1:600 HM Submarine Porpoise. She was the class prototype, and her mine casing terminated aft
of the stem, giving a saw-tooth appearance. She is seen here in a non-standard camouflage
scheme. © Andrew Arthur
1:600 drawing of the standard class members. The mast and periscopes were off-set to starboard
to clear the mine conveyor belt © Andrew Arthur

These boats used the minelaying system first developed on the M3 minelayer, with the Mark 16 mine. An endless chain fitted inside the extra deep casing discharging the mines over the stern. Because the mine accommodation passed through the conning tower structure periscopes and the conning tower hatches were positioned off  centre to starboard.
These were the last of the purpose built  minelayer as the development of mines that were capable of  being laid from standard 21" torpedo tubes.
Porpoise was a prototype and differed in three main ways - she had a circular pressure hull, the others had oval hulls; she carried all her fuel oil in saddle tanks, the others internally; and her mine casing was not flush with the hull casing for'ard, it terminated before the bow section, giving a saw-toothed appearance.
Rorqual was the only one of the class to survive the war and laid 1284 mines during that period.

Surface Displacement 1768 tons Length 88.09 m
Submerged Displacement 2053 tons Beam 9.09 m
Ballast load 285 tons Draft 4.88 m
Performance & Propulsion
Range 11500 nm @ 8 kts = 48 days
Dive 91 m
Speed 15.5 kts ( 9 kts submerged )
Machinery 2 x Vickers Diesels @ 3300 hp
2 x Electric motors @ 1600 hp
Armament & Complement
Complement 6 officers & 55 ratings
  • Torpedo
    • 6 x 21" bow tubes
    • 12 x 21" torpedoes
  • Mines
    • 50 x Mark 16 mines
  • Gun
    • 1 x 1 x 4" DP
    • 2 x 1 x 0.303" MG AA
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