Commodore Warnaar was bom in May 1964 in Emmeloord, a small town in one of the Dutch poldens. He joined the Netherlands Naval College in 1986 and was commissioned in 1990. Ater completing studies in International Affairs, he served as a Watch Keeper, Navigator and Principal Warfare Officer on various frigates. Returning to shore in 1998, he received assignments as a Surface Warfare Instructor and Navigation Instructor. During that period, he was frequently detached as a Navigation Sea Rider to the training staff of the Netherlands Frigate Squadron and the training staff of the
Naval Mine Warfare group.
Promoted to Lieutenant Commander, Warnaar completed two tours as Head of Operations, on frigate HNLMS Blys van Treslong and frigate HNLMS Philips van Almonde – the first Royal Netherlands Navy unit assigned to Operation Enduring Freedom after the 9/11 attacks. He undertook an extended two-year deployment on board the guard ship in the Caribbean. In 2004 he served in the Caribbean as
staff communications officer. During this assignment, he was involved in several military assistance operations and took command of the support ship HNLMS Pelilaan. After returning to the Netherlands in 2006, he completed tours of duty with Standing NATO Maritime Group 2 (SNMG2), and
as the Executive Officer of the frigate HNLMS Van Amstel.
After promotion to the rank of Commander, he served in the Netherlands Ministry of Defence as head of the Above Water Warfare section in the Naval Requirements branch. He was subsequently involved in anti-piracy operations in the Indian Ocean, before commanding the Oceangoing Patrol Vessel (OPV) HNLMS Friesland.
After promotion to Captain, he headed to the Strategy and Advice (Naval Policy) desk of the RNLN. In 2015 he assumed command of the RNLN Sea Training Command, and commanded the Netherlands Maritime Headquarters in Den Helder from 2019-2024.
Arjen Warnaar is a graduate of the Netherlands Joint Staff course and the Royal College of Defence Studies, London. He is married to Jeannette Koornneef. They have two daughters and live in Friesland.