The interwar sloop opportunity Canada missed

Canada's destroyer purchases raise a broader force-structure question about what the country could have bought in the 1920s and 1930s. Sloops offered a flexible alternative to scarce destroyers because they could perform fishery protection, presence missions, minelaying, minesweeping, training, anti-submarine warfare, and convoy escort. The treaty definition allowed a displacement of up to 2,000 tons, a design speed no greater than 20 knots, no torpedoes, and only a limited number of guns. Those restrictions still left a useful surface combatant particularly well suited to anti-submarine and mine warfare. The Washington and London naval treaty systems did not constrain sloops in the same way as destroyers, so a trade-dependent dominion could have built useful capacity without pursuing a battle fleet. Defence works like insurance here: it looks expensive before a crisis and cannot be improvised once the crisis arrives.