As a result of German research on VTOL fighter design during latter days of WWII (by Focke-Wulf), USAF and Navy initiated Hummingbird project 1947. Next, Navy received design proposals from Lockheed and Convair 1950. 31 May 51 Convair awarded a contract for XFY-1; Jun 51, Lockheed awarded similar contract for XFV-1. Both designed to use C-W engine, but only available engine went to Convair. As a result, XFV-1 made only conventional takeoffs and landings beginning Dec 53 and ending with project's cancellation Jun 55. Operationally, "tail-sitters" envisioned for use on both land and sea. Fears of Russian effort to move into western Europe and deny Allies use of coventional airfields led to search for aircraft that could operate from limited space. Similarly, Navy interested in VTOL capability to permit operations from small carriers or even merchant ships. Pogo made first tethered takeoff and landing in dirigible hangar at Moffett NAS CA and completed first VTOL cycle Nov 54. Project also cancelled at completion of flight test program. (A jet tail-sitter, Ryan X-13 Vertijet, also made successful transition Nov 56; however, project cancelled fall 57.) Short-lived era of tail-sitting VTOL gave way to jet-propelled, fixed- wing, thrust-vectored Harrier made in UK by Hawker-Siddeley. Because it takes off and lands in a conventional horizontal attitude, Harrier overcame some of the most serious drawbacks of tail-sitters including relatively slow speeds and exceptional skills required of pilots.