B-17
A design out of the 30´s, it was a rugged four-engined heavy level bomber with a range/bombload combination which allowed bombing raids against most german cities. The defensive armament consisted of many heavy machine guns and made the USAAF generals believe that fighter escort isn´t necessary. The problem of these bombers was that although their bomb sights were theoretically accurate, bombs falling out of 25,000ft (7520km) and more exploded 1,500ft (500m) away from the target in average.
later B-17G: 6,000lbs (2724kg) bombload over ******miles (3219km) at 25,000ft (7620m) altitude. 13x0.5" (12.7mm) MG, crew: 10, 4x895kW (1200PS), max. ****mph (462km/h)

B-24
Planned as the B-17 successor, this heavy bomber had superior range (and less maneuvrability) due to his Davis-wings. The problems with this type were the same like with the B-17; it needed fighter escort and had poor precision.
later B-24H/J: 5,500lbs (2268kg) bombload over *******miles (3460km) at 25,000ft (7620m) altitude. 10x0.5" (12.7mm) MG, crew: 10, 4x895kW (1200PS), max. *****mph (488km/h)

XB-28
A powerful high-altitude high-speed further development of the B-25, it was in fact a new design. Three prototypes ordered in february, 1940, first one flew in april, 1942. Interesting was that this medium bomber was able to carry the same bombload of the B-17 over a slightly bigger range, with half personnel. It was as modern as the XB-29, could have been operational in late´43 or early ´44.
6,000lbs (2724kg) bombload over 2,040 miles (3283km) at 25,000ft (7620m) altitude. 3x2 + 3 0.5" (12.7mm) MG, crew: 5, 2x1491kW (2028PS), max. 372mph (***km/h) at 25,000 feet, cruise 255mph

XB-29
The later B-29, a more modern heavy bomber, something like a B-24 on steroids. All of these were later needed in the pacific theater, because they alone had sufficient range for bombing Japan.

XB-32
This was an inferior backup to the XB-29.

P-38
A twin-engined heavy fighter. Too less maneuvrable to compete with the german standard fighters, but dangerous if the interceptors concentrate themselves on the bombers. Poor engine reliability, concentrated armament, long range, good durability.
later P-38L: ********mph (666km/h), *****miles (******km), 1x20mm MG + 4x0.5" (12.7mm) MG, 2x1100kW (1496PS)

P-39 and XP-63
These were fighters which had their liquid-coold engine in the center of their fuselage. Their main weapon, a 37mm machine cannon, was the unreliability in person and although excellent arodynamics allowed high speeds with limited engine power, they were useless as escort fighters because they lacked maneuvrability and range.

P-40
A third class fighter at this time. Obsolete even in 1940, the huge production numbers of this type reveal two things;
1. The USAAF had no potent lightweight fighter. P-38, P-49 and P-47 weren´t in the same branch as the successful Spitfires, Bf-109´s and Fw190´s. They bought this instead, and suffered heavy losses.
2. A giant waste of resources (human, material, financial) and time. The USA were lucky that even such wastings weren´t able to reduce the industrial superiority of this biggest industrialized country too much.
Useless against the german air force (Luftwaffe).

P-47
A heavy fighter. A further development of the P-43, this plane was as heavy as some light bombers of this time. The engine was thirsty, so the fuel capacity of this plane was usually insufficient to escort bombers deep into germany (The theoretically possible external fuel capacity reduced air combat capabilities so far that they had to be released at the first contact, making that range as below impractical. In reality, the range was less than the half.). Tactical superiorities of this fighter were heavy armament, absorption of huge damages, high speed, higher dive speed. But 109´s and 190´s were much more maneuvrable.
later P-47D: ******mph (697km/h), 3060km with three external fuel tanks, 8x0.5" (12.7mm) MG, 1x1891kW (2535PS)

A-36 and XP-51B
The ground attack plane called A-36 "Apache", was in fact an early P-51 Mustang with an US liquid-cooled engine which had extremely poor performance at medium and high altitude. Rolls Royce engineers had calculated in 1942 that this airframe could reach ***** mph (697km/h) at ***ft (7772m) if added with a Rolls Royce Merlin engine with two-stage supercharger. North American needed only 102 days for the prototype construction in 1940, the fighter did excellent dogfighting and ground-attack work at low altitude, a Merlin-powered XP-51B prototype flew in november, 1942 and the USAAF needed until mid 1943 for quantity production. This fighter was able to take on german standard fighters one-to-one and to escort bombers deep into germany. later P-51D: ********mph (703km/h), *********miles (3347km) with two external fuel tanks, 6x0.5" (12.7mm) MG, 1x1264kW (1719PS)

XP-75
A Frankenstein fighter, combined the worst of several planes to an ugly monster. Forget about.