DEF STAN 59-411 is a British Defense Standard that defines the requirements for electromagnetic compatibility (EMC) of electrical and electronic equipment used for military activity. 

It consists of five parts:

• Part 1: Management and Planning
• Part 2: The Electric, Magnetic, and Electromagnetic Environment
• Part 3: Test Methods and Limits for Equipment and Sub-Systems
• Part 4: Platform and System Test and Trials
• Part 5: Code of Practice for Tri-Service Design and Installation

Part 1: Management and Planning - The first part of the standard outlines the specific requirements for electronic devices in EM environment conditions covered in documentation . These documentations confirm that the management techniques and control methods are utilized in acquisition stages of any given project. Certain guidelines for simulated Nuclear Electromagnetic Pule(NEMP), lightning strikes, and ESD tests are also included in this part. This section of the Defence Standard also offers guidance on EMC (Electromagnetic Compatibility) requirements for military equipment and its application across the acquisition process. It covers various aspects, including operational scenarios, contractual requirements, EMC management, testing plans, roles and responsibilities, safety, and more. While primarily focused on EMC, the outlined procedures can be extended to other related disciplines like EMP, RADHAZ, TEMPEST, and ECM, emphasizing commonality for efficient equipment design, management, and testing procedures.

Part 2: The Electric, Magnetic, and Electromagnetic Environment - The second part of the standard describes the typical military EM environment – covering land, sea, and air and includes both stationary and mobile equipment. These environments may be man-made (civil & military) or natural. It focuses on analyzing the strength of electromagnetic fields that could accidentally disrupt al materials. In this standard, the EM Fields encountered by weapon systems (close to the target) or generated by jamming systems are not considered, unless specified/defined by the equipment's user and system requirements. The frequency for the EM environment is limited to 40 GHz. The electromagnetic events discussed here cover a range of phenomena. In the frequency domain, they include static and near-static electric and magnetic fields, communication signals, radar emissions, and conducted emissions. In the time domain, they include occurrences like Electrostatic Discharge (ESD), rapid switching events, Electromagnetic Pulse (EMP), and lightning-related phenomena. However, these sources of EM radiation are not considered as a part of this standard:

• Low power (<10 W) radio communications from a distant transmitter (>100 m);
• Cosmic/solar radiation;
• Terrestrial magnetic field

The description of these environments has been supplied appropriately, but the performance improvement details have not been given.

This section of the Standard acknowledges that using a one-size-fits-all worst-case environment description can result in excessive and impractical levels of protection. To address this, two approaches are considered. The first involves providing a statistical description of the field, which is complex and scenario-dependent. The second approach, which is adopted here, offers a more practical solution by specifying the maximum likely fields for various operational scenarios. Projects with different scenarios may need to consult specialists to create revised figures. While this approach is more realistic, it may require projects to determine if the scenarios apply to their systems and define additional ones based on transmitter distances and other factors, with guidance from specialists as needed.

Part 3: Test Methods and Limits for Equipment and Sub-Systems - The third part of the DEF STAN 59-411 includes the methodology of measurement of EMC characteristics to lessen the propagation of the EM energy, be it conducted or radiated. It also specifies the limits for equipment and -sub-sub-systems. It applies to various equipment acquired by the Ministry of Defence for all three Services, including items like equipment worn or carried by personnel, portable equipment, line replacement units (LRUs), sub-systems, support equipment, and any specialized EMC test equipment needs.

Part 4: Platform and System Test and Trials - The fourth part of the standard deals with the typical requirement for platform and system tests and trials. Annex A of this standard focuses on the requirements related to the Air Service, particularly when it comes to conducting trials for aircraft before, they can be officially used. Approving an aircraft for service is a very controlled process. If the project follows the MOD Generic Aircraft Release to Service process, a specific authority is responsible for approving the aircraft for service. Before this approval can happen, various tests and assessments, as outlined in Defense Standard 00-970, must be completed. These tests include both theoretical studies and electromagnetic compatibility trials of individual equipment, parts of the aircraft, and the entire aircraft in different setups. While any qualified authority can carry out these assessments and trials, it's common to involve experts in the field who have the necessary facilities for comprehensive aircraft and flight trials. According to this annexure of the part, the EMC testing of the entire aircraft will encompass techniques like low-level swept current (LLSC), bulk current injection (BCI), mode stirring as wellfull threat radiation. The amount of testing required varies based on the type of aircraft, its purpose, and the technologies used in its construction. Annex B of this Standard focuses on the requirements for Land Service equipment. This equipment can include military vehicles, transportable container facilities, and fixed buildings. It also covers portable platforms that can be worn or carried by personnel from all three service branches. The annexure outlines the criteria for conducting EMC in-situ tests on this equipment. These tests involve assessing emissions, susceptibility to external interference, grounding for RF signals, radiation patterns of omnidirectional antennas, and ensuring that onboard interference doesn't degrade communication quality. This annex is relevant for both stationary and mobile equipment and communication systems, including those with obstructed propagation paths. It's applicable during the "Installation Certificate of Design and Performance" phase of procurement, and some parts may apply to production and in-service testing as well. Annex C of this standard comprises the requirements for Sea Service equipment, about ships and submarines. When new ships are built or undergo major maintenance, comprehensive EMC trials are conducted to ensure that all the electronic systems onboard work well together without causing interference. The company responsible for building or maintaining the ship must provide a plan outlining which trials will be performed to meet EMC requirements. This annexure covers testing emissions and susceptibility, Weapon Electronic Mutual Interference Trials (WEMIT), specific EMC trials for submarines, trials related to electronic interference between weapons systems on ships and submarines, and considerations for land-based systems used by the Sea Service. It applies to large sea systems, ship and submarine platforms, and land-based sea systems. The specific application of this Standard for a particular project will be determined by the MOD Project Manager. It also mentions Radiation Hazards (RADHAZ), Electrostatic Discharge (ESD), Nuclear Electromagnetic Pulse (NEMP), armaments, and Electro-Explosive Devices (EEDs) when tests are for a particular service environment.

Part 5: Code of Practice for Tri-Service Design and Installation - The fifth part of the standard titled “Code of Practice for Tri-Service Design and Installation” includes advice for Project Managers and Advisors in MOD on the different phases of electrotechnical equipment installation right from design to service maintenance and modification. Electrotechnical equipment includes equipment installed in Air Platforms, Land Vehicles, Surface Ships, and Submarines This part of the standard is solely intended to provide advice on the electromagnetic compatibility of equipment and systems and their installation, and other aspects including safety, reliability, and maintainability must be taken into account when applying the recommended measures. EMC test methods and limits are covered in Parts 3 and 4 of the Standard. The measures recommended for achieving EMC will also assist in providing Nuclear Electromagnetic Pulse (NEMP) Hardening and lightning (LEMP) hardening. Severe EMC problems are likely to arise in non-metallic platforms i.e., ships, (e.g., glass reinforced plastic) requiring special techniques to be adopted. Specific platform requirements related to the electromagnetic scenario are discussed in the three service annexes as appropriate.