| Abbreviation | Definition |
|---|---|
| Mbps | MegaBits Per Second |
| MBS | Multi-Beam Sonar |
| MC | Marine Commercial |
| MC | Maritime Commission |
| M-CLASS | mobile CLASS |
| M-CLASS | Mobile Cross-chain LORAN Atmospheric Sounding System |
| MCM | Mechanical Current Meter |
| MCS | Mesoscale Convective System |
| MCSST | Multi-Channel Solid State Transmitter |
| MCSST | Multi-Channel SST |
| MCV | Mesoscale Convective Vortex |
| MD | Miscellaneous Debris |
| MDA | Mesocyclone Detection Algorithm |
| MDA | Multi-Decadal Oscillation |
| MDB | Multilateral Development Bank |
| MDC | Mini Drift Chamber |
| MDD | Meteorological Data Distribution |
| MDNB | Maximum Depth for Neutral Buoyancy |
| MDR | Minimum Decompression Rules |
| MDT | Monitored Drift Tube |