He was involved in the development and adoption of numerous weapons, including the M4 Sherman and M26 Pershing tanks, the DUKW amphibious truck, the Bell H-13 Sioux helicopter, and the M16 rifle.

During World War I, he was an instructor at the School of Fire at Fort Sill, Oklahoma and the November 11 armistice ended the fighting before he received orders to go to France.

He was promoted to major general in October 1940 and took command of the newly-formed 9th Infantry Division at Fort Bragg, North Carolina, a base whose construction he oversaw.

He pressed American industry to produce more powerful engines and, often against the views of his superiors, pushed the development of the M4 Sherman, a medium tank with a 75 mm gun.

[4] Growing up in the heart of Pennsylvania Dutch country, the young Jamie Devers, as he was called by his family, enjoyed the outdoors: camping, fishing, and hunting.

Always competitive despite being slightly built, the 120-pound (54 kg) 5-foot-10-inch (178 cm) Devers captained the basketball team, played defensive quarterback in football, and starred in baseball.

[29] During his tour, Devers was credited with making a number of innovative artillery tactical and technical improvements, including advanced fire-support techniques, which was later used successfully during World War II.

There was at the time a genuine fear that a hostile nation might strike at the United States with an attack on the Panama Canal and prevent the movement of ships between the Pacific and the Atlantic.

Devers directed basic and advanced infantry training at Bragg for the thousands of troops under his command: regular army, national guard, reservists, and draftees.

By working closely and co-operatively with engineers, local contractors, quartermasters and staff and by cutting through red tape, Devers oversaw completion of 2,500 buildings and 93 miles (150 km) of roads in six months.

[46] In a major reorganization of the War Department in March 1942, McNair was named Commander of a new component, Army Ground Forces (AGF), which replaced GHQ.

Devers differed by countering that the number of tank "kills" credited to antitank gunners was unrealistic and biased and felt that "we were licked by a set of umpires' rules".

To make matters worse, the designers shortened the barrel to improve the M3's mobility, which Devers realized also reduced the gun's muzzle velocity and hence its effectiveness against armor.

[68] Pressure increased on Devers, who was promoted to lieutenant general (equal in rank to McNair) on 6 September 1942,[39] to push more armored units through the pipeline even more quickly.

[82] On 3 May 1943, while on an aerial inspection tour, Lieutenant General Frank M. Andrews,[84] European Theater of Operations, United States Army (ETOUSA) commander since replacing Eisenhower on 5 February 1943,[85] was killed in an air crash in Iceland.

[88] Devers' main objection to the COSSAC plan was that he did not want American units smaller than corps directly subordinated to British command,[90] based on what he called "the Pershing Principl".

On 28 July 1943, Eisenhower and Lieutenant General Carl Spaatz asked that four groups of Boeing B-17 Flying Fortress bombers be sent to the North African Theater to help support Operation Avalanche, the Allied invasion of Italy.

Operation Shingle, Clark's plan for a surprise end run to outflank the German Winter Line called for Allied landings at Anzio on Italy's west coast, thirty miles south of Rome.

Devers wondered why such a high-level conference was required for what he saw as a simple military decision, but he noted in his diary that "the individuals present all favored an amphibious operation at Anzio".

[110] Major General John P. Lucas' VI Corps did not achieve the desired result at Anzio, and Clark's attempted crossing of the Rapido River was a disaster.

Taking advantage of the German practice of not giving away their positions by firing on small planes, Devers and Eaker flew low over the monastery and saw what they believed to be a radio aerial and enemy soldiers moving in and out.

[115][116] The continuing failure to advance in Italy prompted the Combined Chiefs of Staff to postpone Operation Anvil, the on-again-off-again proposal for Allied landings along the coast of Southern France coinciding with Overlord.

[124] Virtually all of the material needed for the assault was on hand, on the way, or promised because of Devers's efforts to preserve the stockpile of Anvil stores and supplies even when the operation was in doubt.

[132] Devers had written to McNair on 4 February 1944 and noted that when divisions were left in the line for more than 30 to 40 days, fatigue, carelessness, and exposure resulted in increased casualty and sickness rates.

[144] Devers conceded that he could supply Patton with only 1,000 short tons (910 t) per day from 15 November, which only increased Eisenhower's resolve to give priority to opening the port of Antwerp, in the north.

[149] When Eisenhower and Bradley visited 6th Army Group on 24 November, they were astonished to find Devers, Patch, and Haislip energetically planning a crossing of the Rhine in early December.

[152] An attempt to reduce the Colmar Pocket on 15 December was called off by Eisenhower when Bradley was hit by the German Ardennes Offensive,[153] which Brigadier General Garrison H. Davidson, the Seventh Army Engineer, felt might have been avoided entirely if Devers had been allowed to proceed with the Rhine crossing.

[173] Devers hired a civilian secretary, Dorothy Benn, a widow whose husband, an Army Air Forces pilot, had been listed as missing in action in New Guinea in 1943 and was presumed dead until his body was found in 1957.

[183] Finding that the life of a rancher did not sufficiently hold his interest, Devers accepted a job as managing director of the American Automobile Association Foundation for Traffic Safety.

[187] Devers also served briefly in 1951 as military advisor to Frank P. Graham, the United Nations mediator in the dispute between India and Pakistan over the status of Kashmir.