Douglas B - 18 Bolo The Douglas B - 18 Bolo medium bomber served with the United States Army Air Corps and the Royal Canadian Air Force ( as the Douglas Digby ) during the late 1930s and early 1940s . The Bolo was built by Douglas Aircraft Company and based on its DC - 2 and was developed to replace the Martin B - 10 . By 1940 it was considered to be underpowered , to have inadequate defensive armament and carried too small a bomb load . Many were destroyed during the attacks on Pearl Harbor and the Philippines in December 1941 . In 1942 the B - 18 survivors were relegated to antisubmarine or transport duty . A B - 18 was one of the first American aircraft to sink a German U - Boat , the " U - 654 " on 22 August 1942 in the Caribbean . Design and development . In 1934 , the United States Army Air Corps put out a request for a bomber with double the bomb load and range of the Martin B - 10 , which was just entering service as the Army ' s standard bomber . In the evaluation at Wright Field the following year , Douglas showed its DB - 1 . It competed with the Boeing " Model 299 " ( later the Boeing B - 17 Flying Fortress ) and Martin Model 146 . While the Boeing design was clearly superior , the crash of the B - 17 prototype ( caused by taking off with the controls still locked ) removed it from consideration . During the depths of the Great Depression , the lower price of the DB - 1 ( $ 58 , 500 vs . $ 99 , 620 for the Model 299 ) also counted in its favor . The Douglas design was ordered into immediate production in January 1936 as the B - 18 . The DB - 1 design was essentially that of the DC - 2 , with several modifications . The wingspan was greater . The fuselage was deeper , to better accommodate bombs and the six - member crew ; the wings were fixed in the middle of the cross - section rather than to the bottom , but this was due to the deeper fuselage . Added armament included nose , dorsal , and ventral gun turrets . Operational history . The initial contract called for 133 B - 18s ( including DB - 1 ) , using Wright R - 1820 radial engines . The last B - 18 of the run , designated DB - 2 by the company , had a power - operated nose turret . This design did not become standard . Additional contracts in 1937 ( 177 aircraft ) and 1938 ( 40 aircraft ) were for the B - 18A , which had the bombardier ' s position further forward over the nose - gunner ' s station . The B - 18A also used more powerful engines . Deliveries of B - 18s to Army units began in the first half of 1937 , with the first examples being test and evaluation aircraft being turned over to the Materiel Division at Wright Field , Ohio , the Technical Training Command at Chanute Field , Illinois , the Aberdeen Proving Ground , Maryland , and Lowry Field , Colorado . Deliveries to operational groups began in late 1937 , the first being the 7th Bombardment Group at Hamilton Field , California . Production B - 18s , with full military equipment fitted , had a maximum speed of 217 mph , cruising speed of 167 mph , and combat range of 850 miles . By 1940 , most USAAC bomber squadrons were equipped with B - 18s or B - 18As . However , the deficiencies in the B - 18 / B - 18A bomber were becoming readily apparent to almost everyone . In range , in speed , in bomb load , and particularly in defensive armor and armament , the design came up short , and the Air Corps conceded that the aircraft was obsolete and totally unsuited in the long - range bombing role for which it had originally been acquired . To send crews out in such a plane against a well - armed , determined foe would have been nothing short of suicidal . However , in spite of the known shortcomings of the B - 18 / B - 18A , the Douglas aircraft was the most numerous American bomber type deployed outside the continental United States at the time of the attack on Pearl Harbor . It was hoped that the B - 18 could play a stopgap role until more suitable aircraft such as the Boeing B - 17 Flying Fortress and Consolidated B - 24 Liberator became available in quantity . Second World War . When war came to the Pacific , most of the B - 18 / B - 18A aircraft based overseas in the Philippines and in Hawaii were destroyed on the ground in the initial Japanese onslaught . The few Bolos that remained played no significant role in subsequent operations . The Bolos remaining in the continental USA and in the Caribbean were then deployed in a defensive role in anticipation of attacks on the US mainland . These attacks never materialized . B - 17 s supplanted B - 18s in first - line service in 1942 . Following this , 122 B - 18As were modified for anti - submarine warfare . The bombardier was replaced by a search radar with a large radome . Magnetic anomaly detection ( MAD ) equipment was sometimes housed in a tail boom . These aircraft , designated B - 18B , were used in the Caribbean on anti - submarine patrol . Two aircraft were transferred to " Força Aérea Brasileira " in 1942 and used with a provisional conversion training unit set up under the provisions of Lend - Lease . They were later used for anti - submarine patrols . They were struck off charge at the end of the war . In 1940 the Royal Canadian Air Force acquired 20 B - 18As ( designated the " Douglas Digby Mark I " ) , and also used them for patrol duties , being issued to 10 Squadron as quickly as possible to replace the squadron ' s Wapiti ' s . On 2 October 1942 , a B - 18A , piloted by Captain Howard Burhanna Jr . of the 99th Bomb Squadron , depth charged and sank the German U - boat " U - 512 " north of Cayenne , French Guiana . Bolos and Digbys sank an additional two submarines during the course of the war . RCAF Eastern Air Command ( EAC ) Digbys carried out 11 attacks on U - boats . " U - 520 " was confirmed sunk by Flying Officer F . Raymes ' crew of No 10 ( BR ) Sqn , on 30 October 1942 . east of Newfoundland . However , the antisubmarine role was relatively short - lived , and the Bolos were superseded in this role in 1943 by the B - 24 Liberator which had a substantially longer range and a much heavier payload . Surviving USAAF B - 18s ended their useful lives in training and transport roles within the continental United States , and saw no further combat action . Two B - 18As were modified as unarmed cargo transports under the designation C - 58 . At the end of the war , those bombers that were left were sold as surplus on the commercial market . Some postwar B - 18s of various models were operated as cargo or crop - spraying aircraft by commercial operators . Aircraft on display . Only five B - 18s still exist , preserved or under restoration in museums in the United States :