Overseas National Airways (ONA) was a supplemental air carrier (also known as an irregular air carrier or a non-scheduled carrier) during the period in which the Civil Aeronautics Board (CAB), a now defunct United States Federal agency, tightly regulated almost all US commercial air transport. From 1964 onward, supplemental carriers were charter carriers, but until 1964 they were charter-scheduled hybrids. Until 1950, ONA was known as Calasia Air Transport, and until 1947, Air Travel.

ONA was effectively two distinct carriers, separated by a two-year interval in 1963–1965 during which it fell into bankruptcy and became almost completely moribund, after which it was reconstituted by new ownership/management. From 1969 through the mid-1970s, ONA was one of the largest charter carriers in the United States, engaged in diverse activities including building the Mississippi Queen paddlewheel riverboat. However, in its last years the carrier faced increasing competition, uncertainty and poor financial results and in 1975–1977 suffered the loss of three aircraft in accidents within a 16-month period, including two DC-10s within two months. The carrier chose to liquidate in 1978 outside bankruptcy.

San Francisco-based Air Travel was incorporated in California on May 18, 1946 by George W. Tompkins, a former World War II Navy transport pilot who obtained a war surplus C-54 through preferences for returning veterans. In 1947, Air Travel became Calasia Air Transport. The carrier was issued its "Letter of Registration" on 12 August 1947 (in lieu of certificate, as was standard for irregular airlines at the time). Also in 1947, Calasia started operating its fleet of five leased C-54s under contract to Transocean Air Lines until January 1950. In July 1950, Overseas National Airways was incorporated in Delaware, and ONA started operating in the Pacific under contract to the Military Air Transport Service (MATS) (North Korean troops crossed into South Korea on June 25, 1950). In 1954, ONA was an applicant in a CAB case in which Seaboard & Western Airlines was certificated as a scheduled transatlantic cargo carrier. ONA was judged able but not as able as Seaboard, which, based on 1953 data was about three times the size of ONA, whether by fleet (12 DC-4s vs 4) or revenues. ONA's 1953 revenue was 100% military, split 52/48 passenger/cargo.

The CAB tightly regulated almost all commercial air transportation in the US, intentionally suppressing competition including regulating all fares as well as determining where scheduled airlines flew.

Until 1960, a major exception in this regime were military charter contracts, which were competitively bid. The CAB had to accept this situation because the US military permitted so-called Part 45 carriers to bid for military charters. Part 45 airlines were not common carriers (did not offer services to the public), and thus escaped CAB regulation. Any attempt by the CAB to impose minimum military charter bids on CAB-regulated carriers could be undercut by Part 45s. Thus military charters were a competitive free-for all. In 1959, for instance, the US military invited 97 carriers to bid for charter work.

This was relevant to ONA because until 1963, it was almost entirely a military charter carrier. In only three years did it have significant civil (commercial) business (see Table 1), including running 140 transatlantic charters in 1959. Once the Korean War was over in 1953, ONA was unable to sustain its financial performance which degraded substantially by the end of the decade. In 1959 ONA bid so aggressively for international MATS contracts that it won over half the awards by dollar value, stripping Trans World Airlines (TWA) and Pan Am of their former MATS business. To handle the volume, ONA leased nine DC-7s to augment its core fleet of four DC-6s. As Table 1 shows, 1960 ONA revenue increased dramatically from 1959, but it also suffered a substantial loss.

ONA's 1960 gambit contributed to a substantial change in military charter contracting. US scheduled carriers had long been unhappy with competitive MATS bidding. ONA's audacious bid motivated TWA, Pan Am and others to press their case with the military, Congress and the CAB. Separately, in February 1960, a report to President Eisenhower recommended, among other things, and the President approved, that Part 45 carriers be excluded from international MATS bidding. With Part 45s no longer a factor, in July 1960 the CAB said it no longer accept competitive bidding for military business. The CAB duly set a minimum rate for international MATS flying. With price no longer a variable, MATS ranked bidders according to their ability to provide (1) turbine (jet or turboprop) equipment with cargo capability, (2) turbine equipment (3) piston equipment with cargo capability in that order. In 1960, no supplemental carrier had long-range turbine equipment (even in 1964, all supplementals together had only six such aircraft, against 427 among the scheduled carriers) so this substantially advantaged the scheduled carriers. When the first set of bids was announced later in 1960 subject to these criteria, Pan Am was on top with 20.5% of the dollar value and TWA was second with 18.6%. ONA's share was 8.5%.

ONA of this era had its main operational base at Oakland, a smaller base in New York and a small headquarters in Washington, DC.