When Cessna introduced its Model 310 light twin aircraft in 1954, it was arguably the sexiest twin-engine aircraft on the market. It was fast, good-looking, and offered the comfort needed by business executives looking to move up from the cabin-class singles like Cessna's own Model 195. Cessna test pilot Hank Waring completed the maiden flight of the first prototype Model 310 on 3 January 1953, and the FAA certified the aircraft in March 1954. Cessna delivered the first 310s in April. In 1955, Cessna's commercial aircraft sales increased almost 50 percent over the previous year, an increase attributed primarily to the new twin. Commercial sales almost doubled in 1956, and again the Model 310 was a pacesetter. By the time the last Cessna 310R was delivered in 1981, Cessna had produced nearly 5,500 of the sleek, fast, sturdy twins. The aircraft achieved a certain popular recognition when the successful '50s weekly television series, "Sky King," chose the 310 as the aeronautical co-star Songbird. In fact, there were three different aircraft used over the several years the show was produced—a civilianized UC-78 Bobcat (Songbird), a 1958 Cessna 310B (Songbird II), and a 1960 310D (Songbird III).

Following the 310's excellent acceptance and outstanding performance in the civilian market, the USAF selected it for administrative, liaison, and light cargo duties as a utility transport. In 1957, the USAF ordered 80 Model 310A aircraft to replace aging Beech C-45s, designating them the L-27A (s/n 57-5846 through 57-5925). All 80 were delivered in 1957, and USAF followed up the next year with a second order for 80 more L-27A aircraft (s/n 58-2107 through 58-2186).

A final contract was issued in 1960 for 35 Model 310E (L-27B) aircraft (s/n 60-6047 through 60-6081). The average fly-away cost of an L-27 under these military contracts was $56,000. All L-27A and L-27B aircraft accommodated a pilot plus four passengers—one in the right front seat and three in the rear bench seat. Although equipped with full dual controls, U-3s were most often flown by a single pilot. In 1962, the L-27A was redesignated as the U-3A, the L-27B as the U-3B.

The original U-3A aircraft were powered by six-cylinder Continental O-470-M engines producing 240 horsepower at 2600 RPM. Maximum gross weight was limited to 4,830 pounds. The U-3B aircraft were powered by fuel-injected six-cylinder Continental IO-470-D engines producing 260 horsepower at 2625 RPM. Maximum gross weight for the U-3B was 4,990 pounds. Besides the engines, the main differences between the two models were the addition of wing de-icing and propeller anti-icing equipment, more sophisticated radio and navigation equipment, an aft-swept vertical tail, and a third side window on each side on the later model. Many of the earlier U-3A versions were later modified to incorporate the U-3B's all-weather gear.

The USAF distinctive blue paint scheme for the U-3 in its utility transport role quickly led to the unofficial, but universally recognized, nickname of "Blue Canoe." In 1960, 25 L-27A Blue Canoes were transferred to the US Army. Later, the Army acquired 13 U-3Bs from the USAF. In the late '50s, the US Navy acquired eight U-3As from the USAF and two from the Army, assigning them BuNos 159073, 159074, 528176, 575849, 575891, 575916, 582111, 582123, 582131, and 582176. In the early '60s, the Navy acquired two more U-3Bs from the Army, assigning them BuNos 606047 and 606068. Despite the application of service-unique paint schemes on the Army and Navy aircraft, the U-3A/B will be known forever as the Blue Canoe.