Design was complete by mid-April, and a contract for 2,000 Mark 18s, 2,020 warheads, 543 exercise heads (for training shots), tools, spares, and workshop gear was issued 2 May.

[7] The batteries (provided by Exide)[8] did not deliver hoped-for performance and gave off too much hydrogen gas[5] (a fire hazard shipboard, and potentially lethal in submarines), and there were bugs in production, in part because of the fine tolerances necessary and the need to use unskilled labor.

[13] Sands "experienced enough torpedo problems to drive an ordinary man berserk": one sank, one broached and ran wild, three fishtailed at launch and hit the outer doors before disappearing, and seven missed astern.

[17] The Mark 18 did not produce a wake of bubbles or turbine exhaust pointing back to the submarine firing it – a major advantage in daytime engagements.

The disadvantages were the low speed compared to the Mark 14's 45 kn (83 km/h; 52 mph), the need to regularly withdraw the torpedoes from their tubes for recharging, sensitivity of the batteries to water temperature,[18] and onerous maintenance procedures.