Although armed with six torpedo tubes and a 4-inch deck gun, these large boats were built around a capacity of fifty mines. The class is also known as the Porpoise class. Grampus was the test bed, while Porpoise survived longer. A surfaced endurance of 11,500 nautical miles at 8 knots gave them the reach to lay minefields in a Pacific contingency before an enemy fleet arrived. Their torpedoes could support the ambush or answer targets of opportunity. Most of the class was lost in wartime, which also shows the risk of sending large submarines into contested waters.
Notable Point · 28:53-35:36
Grampus (Porpoise) class submarines in mine warfare
The Grampus class turned a large submarine hull into a long-range minelayer able to place up to fifty mines.