In mid-1940, after Woodring had resigned and the fall of France had revealed the precarious state of the nation's defenses, Franklin D. Roosevelt bypassed Johnson for the position of Secretary of War but instead choosing Henry Stimson.

In 1942, Johnson briefly served as the president's personal representative in India, until an intestinal illness[5] caused him to resign his post and return to the United States.

[7] Secretary Johnson entered office sharing the president's commitment to achieve further military unification and to drastically reduce budget expenditures on defense in favor of other government programs.

[8] Johnson's unwillingness to budget conventional readiness needs for the Army, Navy or Marine Corps soon caused fierce controversies within the upper ranks of the armed forces.

[14][15][16][17] General J. Lawton Collins went even further when testifying before a House Appropriations committee, stating that Truman administration reductions in Army force levels made it more effective.

[19] Johnson welcomed the passage of the 1949 amendments to the National Security Act of 1947, telling an American Legion convention that he was "happy to report ... that 80 percent of the problems that beset unification immediately disappeared when the President signed the bill increasing the authority and the responsibility of the Secretary of Defense."

[19][21][22][23][24] Johnson's defense cuts, which began on April 23, 1949, were accelerated after he announced the cancellation of the 65,000-ton flushdeck aircraft carrier USS United States.

In congressional hearings and other public arenas, the Navy reacted angrily to Johnson's action by openly questioning the ability of the Air Force's latest strategic bomber, the Convair B-36, to penetrate Soviet airspace.

A relative failure as a strategic nuclear deterrent, the large aircraft carrier would prove invaluable as an element of conventional rapid deployment tactical air forces, requiring neither overflight permissions or overseas basing rights with host nations.

The successors to the canceled supercarrier, the new Forrestal-class aircraft carriers, and later designs, continue in service with the US Navy into the 21st century, forming the core of its offensive striking power.

[9][19] To cheaply rectify the issue, Johnson oversaw the unpopular seizure of the ocean liner SS United States to convert her to a troop transport.

This was the second time Johnson intervened with the shipyard, as the cancelation of the aircraft carrier United States allowed the ocean liner of the same name to begin construction in the same drydock.

[25] In June 1949, the House Committee on Armed Services launched an investigation into charges, emanating unofficially from Navy sources, of malfeasance in office against Johnson and Secretary of the Air Force W. Stuart Symington.

The hearings also looked into the capability of the B-36, the cancellation of the supercarrier United States and JCS procedures on weapons development, and ultimately examined the whole course of unification.

In addition to disparaging the B-36, Navy representatives questioned the current US military plan for immediate use of atomic weapons against large urban areas when a war started.

In its final report, the House Armed Services Committee found no substance to the charges relating to Johnson's and Symington's roles in aircraft procurement.

On the cancelation of the supercarrier, the committee questioned the qualifications of the Army and Air Force chiefs of staff, who had testified in support of Johnson's decision, to determine vessels appropriate for the Navy.

Finally, the committee condemned the dismissal of Admiral Louis E. Denfeld, the Chief of Naval Operations, who accepted cancellation of the supercarrier but testified critically on defense planning and administration of unification.

The House Armed Services Committee concluded that Denfeld's removal by Matthews was a reprisal because of Denfield's testimony and a challenge to effective representative government.

Notwithstanding Johnson's emphasis on unification, it was debatable how far it had really progressed, given the bitter recriminations exchanged by the Air Force and the Navy during the controversy, which went far beyond the initial question of the supercarrier to more fundamental issues of strategic doctrine, service roles and missions, and the authority of the secretary of defense.

Most historians attribute Johnson's efforts to significantly reduce, if not eliminate, US naval aviation in both the Navy and Marine Corps as one of the important factors in bringing about the invasion of South Korea, supported by both China and the Soviet Union.

As a result, all air support during those disastrous months came from USS Valley Forge, the only aircraft carrier left in the Western Pacific when South Korea was invaded.

A week after Johnson took office, the United States and 11 other nations signed the North Atlantic Treaty, creating a regional organization that became the heart of a comprehensive collective security system.

That event and the almost-concurrent retreat of the Kuomintang regime from Mainland China hastened debate within the administration as to whether the United States should develop a hydrogen bomb.

[24] Concluding that the hydrogen bomb was now required as deterrent as well as an offensive weapon, on January 31, 1950, Truman decided to proceed with development, which was supported by Johnson.

Truman was less than enthusiastic about the large defense cost projections for NSC 68 and its implications for existing domestic budgetary spending priorities, and initially sent it back without comment to its authors for further analysis.

[9] Ironically, only the US Marine Corps, whose commanders had stored and maintained their World War II surplus inventories of equipment and weapons, proved ready for deployment though they still were woefully under-strength[28] and in need of suitable landing craft to practice amphibious operations (Johnson had transferred most of the remaining craft from the Navy and reserved them for use in training Army units).

"[33] The US reverses in Korea and the continued priority accorded to European security resulted in rapid, substantive changes in US defense policies, including a long-term expansion of the armed forces and increased emphasis on military assistance to US allies.