An Electromagnetic Masking (EMM or Electro-Magnetic Masking) package hides a craft's electromagnetic emissions in all bands (radio, IR, visible, UV, X-Ray), thus rendering it invisible to passive EMS.
- It is a countermeasure against Sensors.
- It may be referred to as "Stealth Technology".
- It is an electronic device that is a kind of Ship Equipment.
- EMM is an advanced form of stealth design, and includes radiators to dissipate immense IR signatures as well as more advanced electromagnetic absorbing material.
- An EMM package does not mask any active electromagnetic sensors or emissions. It does not mask the craft from active sensor scans conducted by other craft.
EMM Stealth Methodologies
The EMM package is applied across the whole of the hull and may include features such as camouflage patterns (to counter optical sensors such as binoculars), angled surfaces, energy absorbent materials, prismatic or reflec surfaces, physical masking and shielding, and cooling systems.
- It is a passive system.
Electromagnetic Masking (EMM): Ships which are equipped with electromagnetic masking (EMM) packages reduce the effectiveness of active and passive sensors which are used against them. EMM not only disguises a vessel's passive (heat) signature, it also includes the use of stealthy materials to reduce the echo of active sensor energy, and so EMM on the target creates more difficulty for both active and passive detection attempts. 
- EMM is an evolutionary design and is available from very early tech levels. Aspects of EMM are added to the package as new designs of sensor become available.
- Prototype EMM may be available at lower TLs.