The LB-6/LB-7 was the first operational service model of a 13,000 lb (5,897 kg) twin-tail biplane bomber of a series produced by Keystone.

[1] Big Bomber to be Refueled during Flight "The huge twin-motored army bomber (sic) which will take off from Dayton, O., fly to New York City and be refueled while in midair, after which she will drop bomb flares on the city and make a return flight to the Dayton army field.

The nine remaining LB-6s were sent to the 23rd and 72nd Bomb Squadrons, attached to 5th Composite Group at Luke Field, Hawaii, between July and September 1929.

In May 1930 three LB-6s were re-engined to become LB-7s and transferred to the 25th Bomb Squadron of the 6th Composite Group based at France Field in the Panama Canal Zone, where they were all written off in 1931.

Beginning in March 1931 the surviving bombers in the Continental United States were taken out of front-line service, re-designated the ZLB-6 and ZLB-7, and sent to the 40th School Squadron at Kelly Field, Texas, where all were scrapped or surveyed by April 1935.