Keywords: P4M-1s VP-21 NAN2-51.jpg Five Martin P4M-1 Mercators of U S Navy patrol squadron VP-21 in flight in 1950 U S Navy Naval Aviation News February 1951 http //www history navy mil/nan/backissues/1950s/1951/Feb51 pdf 1950 USN PD-USGov-Military-Navy Martin P4M Mercator Patrol Squadron 21 United States Navy |