Isaac Rapp Brush (November 7, 1889 – March 6, 1958) was a decorated officer in United States Army with the rank of Major General.

Brush commanded the 40th Infantry Division from 1942 to 1945 during its World War II involvement in the United States armed forces' liberation of the Philippines.

A maternal grandfather, Isaac Rapp was also a Civil war veteran who served for Union as Second Lieutenant with Company "D", 81st Illinois Infantry.

Brush then entered the University of Illinois in Chicago, but left the college after he successfully passed the Officers' military examinations at Fort Leavenworth in February 1911.

Brush completed the training few months later and embarked for the Philippines, where he joined Company "K", 8th Infantry Regiment at Pettit Barracks, Mindanao.

In July 1915, Brush was transferred to the United States Disciplinary Barracks at Fort Leavenworth, Kansas, and joined First Company of local Guard Battalion.

He was promoted to first lieutenant in July 1916 and assumed duty as Adjutant of 1st Disciplinary Battalion at Fort Leavenworth under Major Dwight W. Ryther.

Brush participated in the training of new recruits and formation of new units at Camps Pike and Wadsworth, South Carolina, and did not deployed overseas during World War I.

[6] In September 1925, Brush was ordered to the Army War College in Washington, D.C., and upon graduation following June, he assumed duty as Commanding Officer, 2nd Battalion, 13th Infantry Regiment at Fort Devens, Massachusetts.

He was later transferred to the Fort Strong, Massachusetts and served as Commanding Officer, 1st Battalion his regiment until August 1927, when returned to Washington, D.C. Brush was subsequently assigned to the Office of the Assistant Chief of Staff for Operations (G-3) and served consecutively under Brigadier generals Frank Parker and Edward L. King until May 1931, when he was transferred to Vancouver Barracks, Washington for duty with 7th Infantry Regiment.

Brush was stationed at Schofield Barracks at the time of the Japanese air attack on 7 December 1941, which brought the United States into World War II, and began organizing the 25th Infantry Division for moving to beach positions for the defense of Honolulu and Ewa Point.

The 40th Division was tasked with the defense of outer islands of Hawaii while Brush assumed additional duty as Commanding general, Kauai District.

The Japanese resisted stubbornly, aided by booby-trapped terrain, defended their fortified positions by day, and conducted harassing attacks at night.

Soon, the 40th Division started using small infiltrating units to creep past tank traps and minefields, then scrambled uphill across open fields of fire to attack Japanese positions.

[10][9][3][12] The capture of Negros Island was completed on June 2, 1945, and Lieutenant General Robert L. Eichelberger, commander of the Eighth Army, praised Brush and his division, decorating him with the Silver Star for bravery.

[13][9][3] The Fortieth Division then returned under command of Sixth Army of Lieutenant General Walter Krueger and was assigned to Charles P. Hall's XI Corps in July 1945.