||1,768 tons (Porpoise), 1,810 tons (others) surfaced
2,035 tons (Porpoise), 2,157 tons (others) submerged
||289 ft (88 m) (Porpoise), 293 ft (89 m) (others)
||29 ft 10 in (9.09 m) (Porpoise), 25 ft 6 in (7.77 m) (others)
||15 ft 10 in (4.83 m) (Porpoise), 16 ft 10 in (5.13 m) (others)
||2 shaft, Diesel (3300 hp) plus electric (1630 hp)
||15.5 knots surfaced
8.75 knots submerged
6 x 21 in torpedo tubes (bow)
1 x QF 4-inch (101.6 mm) Mk XII deck gun
The Grampus-class submarines were a group of minelaying submarines built for the Royal Navy in the late 1930s. These boats are sometimes referred to as the Porpoise class from the single prototype, HMS Porpoise built in 1932. Five boats to a modified design were built between 1936 and 1938. The ships were all named after marine mammals.
The mines were stored in a special "gallery" with a conveyor belt built into the outer casing as pioneered by the converted M-class submarine HMS M3. These boats were of a saddle tank type.
They were used extensively in the Mediterranean, particularly to supply the besieged island of Malta in a service nicknamed the "magic carpet".
Only one, HMS Rorqual, survived the war.
Boats in class 
See also 
Media related to Grampus-class submarine at Wikimedia Commons
Coordinates: 37°05′N 17°30′E / 37.083°N 17.500°E