ISR Glossary of Terms


Any change in the hull, machinery, equipment, or fittings that involves a change in design, materials, number, location, or relationship of any assembly’s component parts whether the change is separate from, incidental to, or in conjunction with repairs.


Scheduled assignment of a ship to an industrial activity for the purpose of accomplishing repairs or performing maintenance and/or modernization. Specific types of availabilities assigned ships are:

Depot Modernization Period (DMP) - An industrial availability for accomplishment of major high priority warfare improvement alterations and such essential maintenance as necessary to ensure unrestricted operations to design test depth. A DMP is designed to increase SSN fleet operational availability by replacing the first non-refueling ROH for SSN 700-718.

Drydocking Phased Maintenance Availability (DPMA) - A phased maintenance availability extended to include drydocking of the ship.

Drydocking Selected Restricted Availability (SRA) - A selected restricted availability extended to include drydocking of the ship.

Extended Refit Period (ERP) - a 60 day planned availability for SSBNs scheduled approximately 4 1/2 and 7 1/2 years after overhaul to accommodate accomplishment of major industrial and intermediate level work items.

Fitting Out Availability (FOA) - An availability at the shipyard designated as the fitting out activity to place onboard the material specified in the ship’s allowance lists.

Intermediate Maintenance Availability (IMAV) An availability at an Intermediate Maintenance Activity for the accomplishment of repairs and modernization. These availabilities may be scheduled or emergent. During these availabilities, the ship may be rendered incapable of fully performing its assigned mission and tasks because of the nature of the repair work.

Phased Maintenance Availability (PMA) - A short, labor intensive availability for the accomplishment of general repairs and modernization by industrial activities. Ships assigned to Phase Maintenance Programs are maintained through PMAs in lieu of Regular Overhaul (ROHs).

Post Shakedown Availability (PSA) - An availability assigned to newly built, activated or converted ships upon completion of a shakedown cruise. The PSA will normally be of 1 1/2 - 4 months duration and will be completed no later than the end of the eleventh month after completion of fitting out at which time Ship Construction, Navy (SCN) funding and work authority terminates. Work performed shall be limited to correcting defects noted during the shakedown cruise and those remaining from Acceptance Trails.

Restricted Availability (RAV) - An availability assigned for the accomplishment of specific items of work by an industrial activity during which the ship is rendered incapable of fully performing its assigned missions and tasks. Restricted Availabilities are assigned by Type Commanders.

Selected Restricted Availability (SRA) - An availability scheduled by the CNO for the accomplishment of repairs and selected alterations by industrial activities sometimes coinciding with intermediate level maintenance. These short, labor-intensive availabilities are assigned to accomplish work that is required to sustain the material condition of the ship between overhauls, particularly those ships on extended operating cycles. They are scheduled sufficiently in advance to ensure advanced planning time and funds are effectively utilized.

Technical Availability (TAV) - An availability for the accomplishment of specific items of work by a repair activity, during which the ship’s ability to fully perform its assigned mission and tasks is not affected.

Voyage Repairs - Emergency work necessary to repair damage sustained by a ship to enable the ship to continue on its mission and which can be accomplished without requiring a change in the ship’s operating schedule.

Depot Level Maintenance

Maintenance which requires skills and facilities beyond the level of the organizational and intermediate levels and is performed at Naval shipyards, private shipyards, SRFs or other shore-based activities. Approved alterations and modifications which update and improve the ship’s military and technical capabilities are also accomplished.

Design Services Allocation (DSA)

The Design Services Allocation is a funding line which provides for design and SHIPALT development work including SAR, SID, MDS, LAR, and SSR update including Configuration Overhaul Planning (COP).

Fleet Modernization Program (FMP)

The Fleet Modernization Program provides the management structure by which the characteristics of ships of the active and reserve fleets are improved. Changes to ship characteristics are accomplished by SHIPALTs, MACHALTs, ORDALTs, or Field Changes and are developed and installed when military, survivability, or technical characteristic considerations dictate ship configuration changes.

Incidental Materials (IM)

IM are any Ship Alteration (SHIPALT) material requisitioned, fabricated or locally procured by the installing activity that is not listed on the Ship Alteration Record (SAR) Alteration Material list (AML). These materials are locally available off-the-shelf, and logistics support is not required. Installation planning, control and management is the responsibility of the installing activity. IM will normally be chargeable to alteration installation funds and will be requisitioned or purchased by the installing activity. The FMP estimate which is entered in the fleet Modernization Program Management Information System (FMPMIS) for IM must include ‘‘odd cog’’ items plus truly incidental items such as nuts, bolts, etc.

Maintenance Levels

The three levels of ship maintenance are:

Organizational Maintenance - Maintenance which is the responsibility of and performed by the ship on its assigned equipment. Its phases normally consist of inspecting, servicing, lubricating, adjusting, and replacing parts, minor assemblies, and subassemblies.

Intermediate Maintenance - Maintenance which is the responsibility of and performed by designated maintenance activities for direct support of ships. Its phases normally consist of calibration, repair, or replacement of damaged or unserviceable parts, components, or assemblies; the emergency manufacture of nonavailable parts; and the provision of technical assistance.

Depot Maintenance - Maintenance performed on material requiring major overhaul or a complete rebuild of parts, subassemblies and end items, including the manufacture of parts, modifications, testing, and reclamation. Depot maintenance serves to support lower echelons of maintenance by providing technical assistance and performing maintenance beyond their capability. Depot maintenance provides stocks of serviceable equipment by using more extensive facilities for repair than are available in lower level maintenance activities.


A major ship availability established for general maintenance and alterations at a naval shipyard or other shore-based depot-level repair activity. During this period, the ship generally undergoes the installation of alterations and modifications to update its capabilities and large-scale maintenance that cannot be undertaken at other times. The categories of overhauls are:

Baseline Overhaul (BOH) - An overhaul that is designed to restore a ship's subsystems, and equipment to a baseline condition before the ship is placed on an Engineered Operating Cycle (EOC). The intent of the BOH is to provide an extensive overhaul that, together with a well engineered and executed maintenance program, will enable the ship to carry out its mission throughout the operating cycle.

Regular Overhaul (ROH) - An availability for the accomplishment of general repairs and alterations at a naval shipyard, private shipyard, or other shore-based repair activity, normally scheduled in advance and in accordance with an established cycle.

Complex Overhaul (COH) - An overhaul that, due to cost, duration, manpower constraints, or the complexity or interrelationship of the various ship subsystems affected by the overhaul work packages, requires coordination and extensive management of both the planning and industrial phases of the overhaul in order to provide a high level of confidence that the overhaul can be satisfactorily completed.

Integrated Logistic Overhaul (ILO) - The work involved in improving the material readiness of a ship by bringing storeroom repair part inventories up to the level prescribed in updated allowance and load lists or to the endurance level prescribed by appropriate fleet authority. Attainment of this broad objective requires the successful conduct of many separate but related actions.

PERA (Planning and Engineering for Repairs and Alterations)

A program for improving the advance planning, integration, and control procedures associated with an availability. The primary objective of the PERA program is to provide intensive management for the accomplishment of effective, efficient, orderly, and timely ship availabilities.

The PERA offices, as extensions of the NAVSEA program manager, integrate the requirements of the various systems and Type Commanders and manage the planning and engineering efforts for availabilities of assigned ship type and vital interrelated programs pertaining thereto. On the basis of ship modernization planning documents, they assist the program managers and TYCOMs in the development of modernization and maintenance packages for assigned ships. The PERAs develop a complete and integrated ship availability planning work package that is usable by an overhaul activity with minimum additional planning.

Ship Alteration (SHIPALT)

Any change in the hull, machinery, equipment, or fittings which involves change in design, materials, number, location, or relationship of the component parts of an assembly. SHIPALTs are classified by title, such as Title "D" alteration (see SHIPALT Titles).


For VAMOSC purposes, "underway" is the condition of a ship consuming fuel in its main propulsion system to drive the ship through the water. A "not underway" status is defined as a ship consuming fuel in its main propulsion system to provide essential electrical, refrigeration, and climate control services but not driving the ship through the water. "Auxiliaries" is defined as the condition in which an auxiliary power generator is consuming fuel to provide electrical, refrigeration, and climate control services while the main propulsion plant is not operating and consumes no fuel.