A Union Army veteran of the American Civil War, Haskin took part in the quashing of the 1866 and 1870 Fenian raids, when Irish nationalists attempted to organize in the United States, then invade the British dominion of Canada.

When the United States Military Government in Cuba ended in 1902, Haskin was appointed to command all U.S. forces remaining on the island.

In 1903, the U.S. Congress passed legislation permitting Union Army veterans still on active duty at ranks below brigadier general to be advanced one grade.

[2] In June 1866, Haskin was part of the Army contingent sent to Malone, New York in response to a planned Fenian raid.

[5] In 1866, Fenians attempted to organize and equip themselves at sites along the Canada–United States border prior to crossing into Canada.

[2] In 1877, Haskin performed duty in Pittsburgh and Reading, Pennsylvania during the government's response to labor unrest that occurred as part of the Great Railroad Strike of 1877.

[2] In 1889, he served on an Army board that conducted reconnaissance of several California ports in order to make recommendations for defending them with coast artillery.

[2] From July to September 1889, Haskin commanded a light artillery battalion during a summer training encampment in northern California.

[2] In 1890, Haskin was assigned to command the post at Fort Columbus, New York, which was garrisoned by three batteries of the 1st Field Artillery.

[6] He was active in the creation of the Military Service Institution of the United States, and was one of the editors of its bimonthly magazine.

[9] In December 1896, a volume Haskin co-authored was published, The Army of the United States, 1789-1896, which he wrote in partnership with Theophilus Francis Rodenbough.

[13] During the Spanish–American War, Haskin was assigned to command the coast artillery positions at Fort Schuyler and Willets Point.

[15] After assuming command of the 2nd Field Artillery, Haskin was posted to Havana as part of the United States Military Government in Cuba.

[20] In July 1903, the U.S. Congress passed a law permitting Union Army veterans still on active duty at the rank of colonel or lower to be advanced one grade.