Though equipped with inadequate defensive armament and underpowered, the Bolo remained the Air Corps' primary bomber into 1941, and the Japanese destroyed some B-18s during the surprise attacks on Dec. 7. By early 1942, improved bombers like the B-17 replaced the Bolo as first-line bombardment aircraft. Many B-18s were then used as transports, or modified as B-18Bs for anti-submarine duty. Stationed at Wright Field from 1939 to 1942, the B-18A on display was acquired and restored by the museum i