after world war ii, reduced budgets meant the coast guard continued to use its two existing wooden 52' mlbs, also known as the type f lifeboats, "invincible" and "triumph". by the late 1950s, the wooden mlbs were starting to wear out and the coast guard built a set of steel 52' mlbs at curtis bay yard to replace them, specifically designed for the high surf conditions encountered along the pacific northwest coast. the steel 52' mlbs feature an aluminum superstructure and a hull divided into seven watertight compartments; because of their relatively high cost of each, only four were built. after entering service, the steering/rudder system was modified by removing the rudder guard, shortening the bilge keels, installing twin rudders, and adding a hydraulic power assist to the steering.