Wikipedia:K-37 trailer

The K-37 trailer was used by the U.S. Army Signal Corps to haul telephone poles, and Cable reel, during and after World War II.

specifications
The K-37 trailer could be configured to haul telephone poles, or wire reel for line construction. Its gross weight was 12.000 Lbs. and was towed by the 1.5-ton K-42, K-43, or k-44 telephone construction trucks. after World War II it was upgraded and renamed the M310. the primary manufacturer was the Highway Trailer Co. of Edgerton, Wisconsin