The system of sheaves at the top of an oil derrick through which lines run to support the loads sustained by the derrick.
(YO-48: dp. 1,731 (f.); 1. 235'; b. 37'; cl. Bullwheel) Crownblock (YO-48) was launched 14 February 1942 by Basalt Rock Co., Inc., Napa, Calif.; and commisioned 28 August 1942, Lieutenant A. G. Popkin, USNR, in command.
Crownblock arrived at Pearl Harbor 23 September 1942 for duty with Service Squadron 8. She was based there throughout the war, delivering fuel oil and aviation gasoline to ports in the Hawaiians and to Christmas, Canton, Palmyra, and Johnston islands. She sailed for Eniwetok 13 July 1945, and in September was transferred to Service Squadron 10. On the 8th she departed for Japan to support the occupation forces, remaining there until 9 April 1947.
Homeward bound, Crownblock called at Guam, Eniwetok, Kwajalein, Pearl Harbor, and San Pedro, Calif., en route to the east coast. She arrived at Norfolk 23 March 1948 and there was placed out of commission in reserve 14 September 1948.