The B-17C differed from the earlier B-17 versions in having the gun blisters removed from the sides of the rear fuselage and replaced by flush, oval-shaped windows. Each of the oval windows had a port for a single 0.50-inch machine gun cut into its edge. The belly gun blister was replaced by a larger metal "bathtub" housing carrying a single 0.50-inch machine gun. The dorsal blister located at the radio operator's position behind the pilot's compartment was replaced by a flush panel into which a single socket for a 0.50-inch machine gun was cut. The nose gun mounting was changed from a single socket in the forward window to six sockets mounted in side windows. The nose 0.30-inch machine gun could be fired from any one of these sockets. Self-sealing fuel tanks and armor protection for the crew were introduced. The engines were four supercharged 1200 hp Wright GR-1820-65 (G-205A) Cyclones. Maximum weight was increased to 49,650 pounds.

The first B-17C flew on July 21, 1940, and delivery to the USAAC was completed by November 29. The first B-17C was retained by the company for test purposes.

Twenty B-17Cs were taken off the production line and transferred to Britain under Lend-Lease as the Fortress I. The rest entered service with the USAAC. However all USAAC machines were returned to Boeing in January of 1941 to be modified to B-17D standards.

Boeing B-17C Fortress 40-2042/2079

Specification of B-17C:

Four Wright GR-1820-65 (G-205A) Cyclone radials rated at 1200 hp for takeoff, 100 hp at 25,000 feet.

Maximum speed 323 mph at 25,000 feet.

Cruising speed 250 mph.

Landing speed 84 mph Service ceiling 37,000 feet.

Climb to 10,000 feet in 7.5 minutes.

Range 2400 miles with 4000-pound bombload.

Maximum range 3400 miles.

Dimensions: wingspan 103 feet 9 3/8 inches, length 67 feet 10.6 inches, height 15 feet 5 inches, wing area 1420 square feet.

Weights: 29,021 pounds empty, 39,320 pounds gross, 49,650 pounds maximum.

Armed with four 0.50-inch machine guns and one 0.30-inch machine gun. One each of 0.50-inch guns were carried in dorsal, ventral, and two waist positions, and there was one 0.30-inch machine gun which could be fired from any one of six sockets in the nose. A maximum of 4800 pounds of bombs could be carried in an internal bomb bay.