(Not all that much US content here, ... but, I hope that it still qualifies.)
Martin Model 177 - the Last B-10 Bomber
The Martin Aircraft Corporation was a busy place at the beginning of 1939. Most pressing was the design of the M-179 in response to a January 1939 Air Corps requirement for a fast medium bomber. [1] The less heavily-armed Model 167 had been tested as the XA-22 but was now being prepared for service with France's Armée de l'Air. Somehow, Martin designers also found time to 'tweak' the last of the B-10 developments - the Martin Model 139W for the export market.
Already in production was the Martin 139WH-3 for the ML-KNIL in the Netherlands East Indies. Redesignated, M-166, the M-139WH-3 had revealed that - without major changes - the M-139 series had run its course. As a result, design began on an 'M-166X' export bomber project. To expedite this study, a service B-10B was 'borrowed' back from the USAAC. [2] Work focused on drag-reduction. To that end, the pilot's cabin was supressed into the forward fuselage. Cockpit glazing was continuous with the revised, now-turretless bomb-aimer's position.
The B-10B's rear gunner's canopy was replaced with a retractable turret from the French M-167F attack aircraft. This turret was placed further forward to allow a new position for the radio-operator. This position was further aft and featured a new, fully-retractable belly gun position. In all, defensive armament consisted of three rifle-calibre Browning machine guns. Offensive load was slightly reduced (to 2,000 lbs - usually 4 x 500 lb bombs) and accommodated within a revised, shallower but lengthened bomb-bay.
Top The prototype Martin Model 177X attack bomber, converted from a USAAC B-10B bomber, Middle River, Maryland, April 1939. Note 'unbroken' line of nose glazings and deployed ventral gun position.
The resulting Martin Model 177X was a relatively fast medium bomber which, despite its much larger wing area, was actually lighter than the new M-167F. However, the new forward canopy - with its unbroken line - proved to have a major downside. When flying away from the sun, the pilot could be blinded by light reflecting off the curves of the Plexiglass nose panels. This was unacceptable to potential export customers - particularly the ML-KNIL with its tropical operating environment. Accordingly, a re-design was undertaken and a stepped-down nose devised for the Model 177.
An ML-KNIL order off of the drawing board seemed all but certain when central Dutch authorities intervened. The Netherlands East Indies was instructed to surrender its M-177 order in favour of the domestic Luchtvaartafdeling. The LVa was to receive twelve Model 177H-2 bombers to augment its indigenous Fokker T.V fleet. All would be powered by 1,000 hp Wright R-1820-G-105A engines and be armed with 7.9 mm FN-Browning machine guns. The defensive armament for the M-177H-2 was considerably revised compared to that of the M-177X prototype.
The most noticeable change was the new nose position. This mounted a single gun with somewhat limited traverse and elevation. [3] The M-167F cupola was replaced by the new Martin 230 CH-1 hydraulically-operated turret - capable of full 360° rotation - armed with two 7.9 mm guns. A fourth FN-Browning was mounted to fire through one or other of the radio-operator's two belly hatches (which had replaced the prototype's retractable 'chute' position).
Bottom Production Martin M-177H-2 bomber of 2 BomVA (2 Bombardeervliegtuig Afdeling), LVa, having withdrawn back to Brest-Bretagne but still in its original Dutch markings. Note the radio-operator's open waist/belly gun positions.
The 2 BomVA Martins soon received RAF-style roundels and blue-white-red rudder stripes. [4] However, by July 1940, none of the surviving 2 BomVA Martins were airworthy. On 30 July, 2 BomVA was stood down at Perpignan and its personnel evacuated by sea to Corsica.
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[1] The Model 179 would later accepted as the Air Corps' B-26 Marauder
[2] For purely administrative purposes, the M-177X was redesignated XB-10H by the Air Corps. However, all national markings were quickly removed from the prototype conversion and 'XB-10H' was rarely seen.
[3] The new nose superficially resembled that of the M-179/B-26 bomber but was of a narrower, oval section in contrast with the Marauder's circular section.
[4] For Allied recognition purposes, the 1939 Oranje markings were replaced by roundels. Rather than return to the pre-war Dutch tripartite roundel, markings similar to the RAF Type A roundel was decreed. Some aircraft carried Type A1-style roundels on their fuselages where Dutch orange was substituted for the RAF's yellow surround. Tailstripes consisted of the Netherlands' horizontal tricolour of red, white, and blue (which covered only the upper portion of the Oranje rudder markings).
