Upon completion of his initial Fleet Replacement syllabus and designation as an Electronic Countermeasures Officer (ECMO) at VAQ-129 in September 2001, he was assigned to the Cougars of VAQ-139. While with the Cougars, he served as Information Technology, Quality Assurance, and Training Officer. He completed two Western Pacific (WESTPAC) deployments, participating in Operation ENDURING FREEDOM, SOUTHERN WATCH, and IRAQI FREEDOM. Additionally, in December 2003, he graduated from the Electronic Attack Weapons School. Upon his departure from VAQ-139, he was awarded the VAQ-139 Outstanding Junior Officer Leadership Award.
In March 2005, CDR Gierhart joined the Vikings of VAQ-129 as a Fleet Replacement Instructor. While with the Vikings, he served as Systems Instructor, Daily and Weekly Schedules, NATOPS Unit Evaluator, and as a Carrier Qualification Instructor ECMO.
CDR Gierhart then transferred to NAS Lemoore, CA, in December 2007 to join the staff of Carrier Air Wing ELEVEN as the Training and Readiness and Assistant Operations Officer. Here he completed two WESTPAC deployments, one of which was in support of Operation ENDURING FREEDOM.
In December 2009, CDR Gierhart returned to NAS Whidbey Island, WA, assigned to the Garudas of VAQ-134. While with the Garudas he served as Tactics and Maintenance Department Head, and completed two combat WESTPAC deployments in support of Operation ENDURING FREEDOM and NEW DAWN.
In November 2012, CDR Gierhart reported to the Naval Command and Staff College in Newport, RI where he earned a masters degree in National Security and Strategic Studies. Following his graduation in November 2013, CDR Gierhart reported to the Joint Staff J-5 Directorate in Washington, D.C. Here he advised the Chairman of the Joint Chiefs of Staff on matters of Syria strategy and policy, including operations to defeat the Islamic State of Iraq and the Levant under Operation INHERENT RESOLVE.
CDR Gierhart then reported to VAQ-129 in November 2016 to complete his transition training to EA-18G Growler.
CDR Gierhart has amassed over 3,000 flight hours, 600 combat flight hours, and 760 carrier arrested landings. His personal awards include the Joint Meritorious Service Medal, Individual Action Air Medal (one with Combat Distinguishing device), Strike Flight Air Medal (six), Navy Commendation Medal (four, one with Combat Distinguishing device), Joint Achievement Medal, Navy Achievement Medal (three) and various unit, service and campaign awards.