Governing Policy and Guidance for Determining What Gets Done at Field Level:
DoD Directive 4151.18, Maintenance of Military Materiel provides the overall policy framework for the accomplishment of DoD maintenance. It does not, however, specifically identify what work should be accomplished at the field-level. It should be noted that while the Office of the Secretary of Defense is responsible for establishing overarching DoD maintenance policy, the three Service Secretaries are ultimately responsible for equipping their forces and maintaining their equipment (per 10 U.S.C. 7013 [Army], 10 U.S.C. 8013 [Navy] and 10 U.S.C. 9013 [Air Force]).

DoD Directive 4151.18 requires that maintenance programs allocate tasks to appropriate levels of maintenance (i.e., field and depot) based on criteria derived from warfighter requirements and cost-effective analysis.

DoD Directive 4151.18, Maintenance of Military Materiel (Definitions):

• Field Maintenance Definition: Field-level maintenance is comprised of two sub-levels, shop-type work (Intermediate) as well as on-equipment maintenance (Organizational):

Intermediate Level
Intermediate maintenance is the maintenance level between the most extensive maintenance — depot, and the least extensive (but usually the most common) — organizational.

Joint Publication 1-02, Department of Defense Dictionary of Military and Associated Terms, defines intermediate-level maintenance as that maintenance that is the responsibility of and performed by designated maintenance activities for direct support of using organizations. Its phases normally consist of: calibration, repair, or replacement of damaged or unserviceable parts, components, or assemblies; the emergency manufacture of non-available parts; and providing technical assistance to using organizations.

The Services generally require varying degrees of maintenance capability at different locations. Specifically, maintenance capability at any particular level depends upon mission requirements, force protection, economics of repair, transportation limitations, component reliability, workload agreements, facility requirements, frequency of tasks, and special training required. These requirements exist as Service doctrine that aligns maintenance support structure with the Services' strategic capabilities and objectives.

Organizational Level
Joint Publication 1-02, describes organizational maintenance as that maintenance that is the responsibility of and performed by a using organization on its assigned equipment. Its phases normally consist of inspecting, servicing, lubricating, and adjusting, as well as the replacing of parts, minor assemblies, and subassemblies. Of note is that organizational-level maintenance describes work performed in the field, on the flightline, or at the equipment site, and is not only accomplished by maintenance personnel, but also by equipment operators.

Field-Level Maintenance Workforce*
At the end of FY2015, the four military Services had a field level maintenance workforce of approximately 570,000 personnel.

Major Intermediate Maintenance Activities (Active Component)

Army

• 45 aviation maintenance companies
• 289 ground maintenance companies
• 1 watercraft maintenance company

Navy

• 12 shore-based I-level fleet readiness centers (FRCs)
• 6 shore-based overseas aircraft intermediate maintenance departments (AIMDs)
• 19 shipboard AIMDs
• 8 ship/submarine intermediate maintenance facilities (IMFs)

Air Force

• 57 aircraft, missile, and munitions maintenance groups (MXGs)

Marine Corps

• 11 marine aviation logistics squadrons (MALSs)
• 3 maintenance battalions

Major Intermediate Maintenance Activities (Reserve Components)

Army National Guard

• Maintenance companies: 35 aviation, 309 ground
• Approximately 13,000 civilian maintainers primarily assigned to field maintenance shops, training and support sites, combined support maintenance shops, and aviation support facilities in each state or territory.
• 4 Theater Aviation Sustainment Maintenance Groups (TASMGs)

Army Reserve

• Maintenance companies: 7 aviation, 35 ground, 1 watercraft
• Approximately 2,000 civilian maintainers assigned across the four regional support commands, working primarily at dispersed equipment concentration sites (ECSs), or area maintenance support activity (AMSA) locations.

Navy Reserve

• 4 shore-based I-level FRCs

Air National Guard/Air Force Reserve

• 107 aircraft, missile, and munitions MXGs

Marine Corps Reserve

• 2 MALSs
• I-level maintenance functions reorganized within 2 Combat Logistics Battalions (CLBs)

*(2016 DoD Maintenance Fact Book)