Why France's 138.6 mm destroyer gun underdelivered

The large weapon promised decisive shell effect against destroyers and cruisers. The 1929 model could reach twelve rounds per minute but normally fired about seven, while the 1934 model managed five to nine. A destroyer lacked the turret space, machinery allowance, crew room, and ammunition capacity that let a true light cruiser sustain fire from comparable guns. Mounts limited to 30 degrees of elevation and magazines of roughly 100 rounds per gun further reduced its value as an all-purpose weapon. A proposed alternative was a small cruiser with enough space for a true dual-purpose mounting, able to act as an anti-aircraft, surface-action, or picket ship. That remained a hypothetical use for a weapon compromised in the contre-torpilleur form.