[1] Appointed in January 2007, he is Chief of Staff at NATO's Headquarters Supreme Allied Command Transformation.

Subsequently, he commanded the 1st Regiment of the Royal Canadian Horse Artillery in Lahr, Germany, from 1989 to 1991.

Arp has served in a variety of staff positions in Land Requirements and in Personnel as a major, lieutenant-colonel and colonel in National Defence Headquarters (NDHQ) from 1986–89 and 1991-97.

During the latter period he also served for one year as the Commander Canadian Contingent as well as the deputy chief of staff of operations for the United Nations Assistance Mission in Rwanda from 1994 to 1995.

In January 2007, Lieutenant-General Arp was promoted to his current rank and appointed chief of staff, NATO's Headquarters Supreme Allied Command Transformation in Norfolk, Virginia.