It trains to deploy worldwide to conduct Day/Night air superiority and precision strike sorties employing laser-guided and inertially aided munitions during contingencies and combat.

It was issued Lockheed P-38H Lightnings stock day fighters with no radar or any other equipment for finding the enemy at night.

[5] The squadron and its detachments moved several times throughout New Guinea providing cover for U.S. Army assault landings, shipping reconnaissance while protecting the various new air bases.

[4] In October 1944, squadron personnel moved to the Philippines, and after bitter fighting, established a camp at San Marcelino Field in February 1945.

Once training was completed with the aircraft at George, the squadron and its wing was moved to its permanent duty station, McConnell Air Force Base, Kansas.

[6] At McConnell, the wing took on a NATO commitment, its mission being the delivery of tactical nuclear weapons in case of a war in Europe.

[6] For the next two years, the squadron deployed frequently, performing rotational TDY duties at Incirlik Air Base, Turkey.

On 31 October 1972, the unit moved to Udorn Royal Thai Air Force Base, Thailand, with the 432d Tactical Reconnaissance Wing.

Combat missions continued in Southeast Asia until the cease-fire on 28 January 1973, in Laos until February 1973, and in Cambodia until 15 August 1973.

[4] In December 1975, the 388 Wing moved from Thailand to Hill Air Force Base, and by 30 June 1977, the 421st was combat ready with F-4E Phantom IIs.

On 29 December 1978, the squadron was reduced to zero aircraft, yet remained with the 388th until June 1980 when they received their first General Dynamics F-16 Fighting Falcon.

Squadron deployment locations in the 1980s included Egypt, Oman, Norway, Italy, Ecuador, Denmark, Saudi Arabia, and Kuwait.

With tensions rising in the Middle East the squadron had to adopt this new weapon system very quickly and had to train in very different scenarios then previously flown in a couple of months time.

On 20 March 1991, the 421st redeployed to its home at Hill Air Force Base after distinguishing itself by flying 1,300 combat sorties (1,200 at night) without any losses or battle damage.

[8] Air Combat Command officials announced a stand down and reallocation of flying hours for the rest of the fiscal year 2013 due to mandatory budget cuts.

The across-the board spending cuts, called sequestration, took effect 1 March when Congress failed to agree on a deficit-reduction plan.

[9] This affected the 421st Fighter Squadron with a reduction of its flying hours, placing it into a basic mission capable status from 5 April-30 September 2013.