During World War II, the U.S. Navy built escort carriers in large numbers for patrol work, and scouting and escorting convoys. Escort carriers, based on merchant ship hulls, were smaller than aircraft carriers; escort carrier crews referred to the ships as "Jeep carriers", the press called them "baby flat tops". The escort carriers had lighter armor than aircraft carriers, were slower, had less defensive armament, and less aircraft capacity compared to aircraft carriers. This smaller variant of carriers was designated "CVE"; a common joke amongst crews was "CVE" meant "Combustible, Vulnerable and Expendable".