MIL-STD-1399: Interface Standard for Shipboard Systems
MIL-STD-1399 is a US Department of Defense standard that sets interface requirements for equipment installed on naval vessels. It covers the electrical, mechanical and environmental characteristics that shipboard equipment must be compatible with.
The standard ensures that diverse equipment from different manufacturers can be integrated on naval platforms and keeps operating under the ship motion, electromagnetic and power quality conditions it meets in service.
It is a family of documents rather than one: a basic standard, MIL-STD-1399C of 2 February 1988, and separately issued numbered sections, each read with the basic standard as one document. Sections are revised on their own schedules, so a specification should name both the section and its edition.
MIL-STD-1399 Power Supply Requirements
The power supply sections of MIL-STD-1399 are the most referenced in procurement and design specifications. They define the AC and DC electrical interface characteristics that equipment must accept.
A ship generates and distributes its own power, and every load shares it. Each power section therefore sets two things: the characteristics and tolerances of the ship’s supply, and the requirements and tests that keep user equipment compatible with it, including limits on what the equipment draws back.
Section 300A and 300B: AC Electric Power
Section 300 covers alternating current power. It specifies the voltage, frequency, waveform and power quality characteristics of the ship’s AC supply.
Section 300A defines steady-state and transient limits, including voltage and frequency tolerances, harmonic distortion and voltage unbalance. Section 300B is not a stricter tier for sensitive equipment: it is the next edition of the same section, issued on 24 April 2008 to replace Section 300A of 13 October 1987.
The tiers within Section 300 are power types. Type I at 60 Hz is the standard ship service supply, while Types II and III at 400 Hz need an approved deviation, Type III with tighter tolerances.
| Power type | Voltage | Frequency | When it is used |
|---|---|---|---|
| Type I | 440 V or 115 V | 60 Hz | Standard ship service supply, used unless a deviation is approved |
| Type II | 440 V or 115 V | 400 Hz | Limited applications, approved deviation required |
| Type III | 440 V or 115 V | 400 Hz | Tighter tolerances than Type II, approved deviation required |
For power converter designers and equipment manufacturers, the practical requirement is that the equipment keeps operating correctly through voltage sags, transients and harmonic content during normal ship operations.
Section 300-1 and 300-2: Low and Medium Voltage AC
Section 300-1 is not a DC section. On 25 September 2018 Section 300 was split into two parts: Part 1 (MIL-STD-1399-300-1) for low voltage AC power and Part 2 (MIL-STD-1399-300-2) for medium voltage AC power.
Part 1 supersedes Section 300B, which Notice 1 of the same date cancelled. Part 2 supersedes Section 680, High Voltage Electric Power, Alternating Current, of 20 April 2008. A validation notice issued in 2024 keeps Part 1 in force without a new revision letter.
Contracts written before 2018 often still call up Section 300A or 300B. Equipment is then designed and tested to the edition the contract names, so confirm it before quoting test work.
Section 390: DC Power for Submarines
Direct current is covered in a separate section. Section 390, Electric Power, Direct Current (Other Than Ship’s Battery) for Submarines, dated 2 October 1987, sets the DC interface for submarine equipment. It excludes ship service DC loads connected to the main storage battery.
For low voltage DC more widely, NAVSEA circulated a draft Section 300, Part 4, Low Voltage Electric Power, Direct Current, for review in December 2019. Check its status in ASSIST before naming it in a specification.
Need help or a quotation?
Our ship lighting range covers interior, deck, navigation and search lights for naval vessels. The military marine interior lights, for example, list a 115 V, 60 Hz supply to DOD-STD-1399 (Navy) Section 300, with a multi-voltage version from 12 V DC to 250 V AC.
For a quotation, or help matching a lamp to a ship’s power section, email info@betalight-tactical.com.
Key Sections of MIL-STD-1399
These are the sections most often named for electrical and electronic equipment. Each date is that of the edition shown.
| Section | Title | What It Covers |
|---|---|---|
| Section 300A | Electric Power, Alternating Current (13 October 1987) | Steady-state voltage, frequency, waveform and transient power quality limits. Cancelled. |
| Section 300B | Electric Power, Alternating Current (24 April 2008) | Revision of Section 300A. Cancelled on 25 September 2018 and superseded by Section 300, Part 1. |
| Section 300-1 | Low Voltage Electric Power, Alternating Current (25 September 2018) | Current low voltage AC interface: Type I, II and III power, tolerances and user equipment tests. |
| Section 300-2 | Medium Voltage Electric Power, Alternating Current (25 September 2018) | Medium voltage AC systems. Supersedes Section 680 (2008). |
| Section 390 | Electric Power, Direct Current (Other Than Ship’s Battery) for Submarines (2 October 1987) | DC power interface for submarine equipment, excluding loads on the main storage battery. |
| Section 301A | Ship Motion and Attitude (DOD-STD-1399, 21 July 1986) | Motion and inclination limits that equipment must operate through. |
| Section 407 | DC Magnetic Field Environment (14 July 2022) | Electromagnetic compatibility requirements for the ship’s DC magnetic field. |
Older specifications name the predecessor of Section 407, DOD-STD-1399 Section 070, Part 1, D.C. Magnetic Field Environment, of 26 February 1979. Other sections cover ship services and environments, including compartment ambient conditions (Section 201), weather (Section 302A) and radiation hazards to personnel, fuels and ordnance (Sections 408A and 409A).
MIL-STD-1399 Testing
MIL-STD-1399 compliance is verified through testing that exposes equipment to the interface conditions of each applicable section. For power supply and converter compliance under Section 300, Part 1 (2018), typical tests include:
- Voltage and frequency tolerance: steady-state variation across the full tolerance ranges, tested at the four corners of the limits once the equipment is thermally stable.
- Transients and interruptions: correct operation before, during and after voltage sags, surges and interruptions, including the emergency short (70 ms by default) and extended (2 minutes by default) interruptions.
- Voltage spikes: 12/50 microsecond spikes applied in both polarities at set points on the supply waveform.
- Harmonic content: correct operation with distorted waveforms, and limits on the individual harmonic currents the equipment draws.
- Grounding and insulation: line-to-ground current of no more than 30 mA per line at the fundamental frequency, and insulation resistance of at least 10 megohms.
- Magnetic field exposure: for Section 407, testing that confirms compatibility with the ship’s DC magnetic field.
Equipment destined for naval platforms is typically also tested to MIL-STD-461 for electromagnetic compatibility and MIL-STD-810 for environmental and mechanical durability. Section 300 sets no EMC limits itself, but the MIL-STD-461 CE101 test is often used to measure distortion in the input current.
Frequently Asked Questions
They are successive editions of the same section, not two levels of stringency. Section 300A was issued on 13 October 1987 and amended by Notice 1 in March 1992; Section 300B replaced it on 24 April 2008. Both are now cancelled, and Section 300, Part 1 of 25 September 2018 is the current low voltage AC edition. Procurement specifications usually identify which edition applies, so check the contract before planning tests.
No. MIL-STD-1399 is specifically a naval shipboard standard. Aerospace power converters fall under MIL-STD-704, which defines aircraft electric power characteristics, and RTCA DO-160, which sets environmental conditions and test procedures for airborne equipment. However, power converters designed for naval vessels are sometimes referenced for other maritime platforms with similar power quality characteristics.
The official documents are published through the Defense Logistics Agency ASSIST database. Its public QuickSearch site lists each section as a separate document with its own notices, so search for the section number, for example MIL-STD-1399-300-1, rather than the basic standard. Section 407 carries distribution statement A and can be downloaded freely; check the statement on each section.
A lamp is assessed against the power section for the supply it connects to, usually Section 300, Part 1 for a Type I supply at 115 V or 440 V, 60 Hz, and against Section 407 where the specification sets DC magnetic field susceptibility. The fixture itself is specified separately, in MIL-DTL-16377 (revision J, 30 June 2014), the general specification for shipboard lighting fixtures.