<p>A continuation of the Huff Daland/Keystone bomber range, the XLB-6 (27-344) marked a considerable change. Taking the last LB-5 airframe, Keystone added entirely new wings of straight chord, angular fins in place of the rounded fins of the LB-5 and took a pair of the new 525-hp Wright R-1750-1 Cyclone engines and mounted them between the wings, rather than on top of the lower wing. The greater power and new aerodynamics achieved some advance, and an order for 17 production LB-6s followed (29-011/29-027). These joined the LB-5s flying with the 2nd and 5th Bomb Groups.
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<p>In 1928 the first of the LB-7s joined the bomber force. These were identical to the LB-6 apart from having Pratt & Whitney R-1690-3 Hornet engines. Eighteen were ordered (28-388/28-395, 29-001/29-010), but the last two were completed with different engines, and different designations. 29-009 was fitted with geared 550-hp Pratt & Whitney R-1860-3s to become the LB-8, while 29-010 was finished with the 575-hp Wright R-1750 Cyclone to become the LB-9. Similarly two LB-6s were re-engined: the LB-10 was an LB-6 with R-1750-1s and a single fin, while the LB-11 was an LB-6 with R-1750-3s. This aircraft was further converted to LB-11A standard with geared GIR-750 Cyclones, while a single LB-12 was produced, similar to the LB-7. Further designations in the series covered the LB-10A, LB-13 and LB-14, which were produced and delivered to the Army under the new B (Bomber) category, and are described there.
