For the majority of the war Haskin served as a brigade and division commander in the Department of Washington manning the Defenses of Washington D.C. In 1864 Haskin was in command of the defenses north of the Potomac in the XXII Corps[2] when General Jubal A. Early's Confederate army approached Washington D.C. Haskin had roughly 4,000 troops to man the fortifications within Washington itself.[3] On July 8 General Martin D. Hardin was assigned to take over command from Haskin who reverted to command of the 2nd brigade. During the Battle of Fort Stevens Haskin's brigade occupied the line from Fort Slocum to Fort Totten.[4] For the remainder of the war he was in command of the XXII Corps' artillery.