Few areas of shielding specification cause more confusion than the standards a contract calls out by number. A statement of work that references NSA 65-6 or MIL-STD-285 is pointing at documents that have been withdrawn or superseded for decades, yet the numbers persist in legacy drawings, inherited specifications, and the institutional memory of facilities that were built to them. For a contractor, the risk is real: building or testing to an obsolete standard can mean a shielded enclosure that fails the acceptance the customer actually needs.
The NSA 65-6 shielding standard and MIL-STD-285 belong to the history of secure-facility shielding, not its present. Understanding what each one was, what replaced it, and what contractors actually build and test to today — IEEE 299 for measuring shielding effectiveness and ICD 705 for accrediting secure spaces — is the difference between satisfying a contract and reworking it. This guide traces the lineage so you can read an old spec correctly and translate it into current practice.
What NSA 65-6 Was
NSA 65-6 was an older National Security Agency specification governing the RF shielding of secure facilities and shielded enclosures used by the U.S. government. It defined construction and performance requirements for shielded rooms intended to protect classified information processing, and for many years it was the reference a government shielding contract would cite. It has since been superseded; the National Security Agency no longer maintains NSA 65-6 as the governing document for secure-facility shielding, and current secure-space construction is driven by Intelligence Community Directive (ICD) 705 and the associated TEMPEST framework instead.
The practical consequence is that NSA 65-6 survives mostly as a citation in legacy documentation. A facility commissioned decades ago may have been validated against it, and a renovation specification may still carry the number forward by inheritance. When that happens, the right move is not to reproduce a withdrawn standard but to map its intent — a defined level of RF attenuation for a secure space — onto the current accreditation regime. National Shielding handles this translation as part of its SCIF and ICD 705 secure-facility shielding work.
What MIL-STD-285 Was — and Why IEEE 299 Replaced It
MIL-STD-285, issued in 1956 and titled "Attenuation Measurements for Enclosures, Electromagnetic Shielding, for Electronic Test Purposes," was a military standard defining how to measure the shielding effectiveness of an enclosure. It was a measurement method, not a construction specification — it told you how to verify attenuation, not how to build the room. MIL-STD-285 was officially withdrawn, and the test methodology it pioneered was carried forward and modernized in the commercial standard IEEE 299, which is the document the industry uses today to measure the shielding effectiveness of solid enclosures.
This distinction matters because the two standards do different jobs. MIL-STD-285 (now IEEE 299) answers "how well does this enclosure attenuate fields?" A construction standard answers "how do I build it?" When a legacy spec references MIL-STD-285 for acceptance testing, the modern equivalent is an IEEE 299 survey performed by a qualified test team. Our guide to IEEE 299 shielding effectiveness testing details the frequencies, antenna placements, and pass criteria that the current method applies, and our RF/EMI testing services deliver that measurement to a documented acceptance.
Standards Lineage at a Glance
The table below lays out the principal standards a contractor encounters in this lineage, their status today, what each one covered, and what replaced it. Reading an old specification correctly starts with knowing where each cited number sits on this map.
| Standard | Year / Status | Scope | What Replaced It |
|---|---|---|---|
| MIL-STD-285 | 1956 / Withdrawn | Measurement method for enclosure shielding attenuation (test method only) | IEEE 299 (modern measurement standard) |
| NSA 65-6 | Legacy / Superseded | NSA construction and performance spec for RF-shielded secure facilities | ICD 705 and current TEMPEST guidance (e.g., NSA 94-106 lineage) |
| NSA 94-106 | Legacy / Largely superseded | NSA specification for shielded enclosures, succeeding earlier NSA specs | ICD 705 Technical Specifications and CNSS/TEMPEST documents |
| IEEE 299 | Current | Method for measuring the shielding effectiveness of electromagnetic enclosures | Active — current measurement standard |
| ICD 705 | Current | Construction and accreditation requirements for SCIFs handling SCI | Active — current secure-facility standard |
NSA 94-106 sits between the eras
NSA 94-106 was a later National Security Agency specification for shielded enclosures that succeeded earlier NSA documents in the 65-series lineage. Like NSA 65-6, it has been largely overtaken by the move to ICD 705 as the governing accreditation framework for sensitive compartmented information facilities, with shielding performance for those spaces now driven by the project's specific TEMPEST determination rather than a single blanket enclosure spec. A contractor seeing NSA 94-106 in a document should treat it as a legacy reference and confirm the current accreditation basis with the accrediting authority.
What Contractors Actually Build and Test To Today
Strip away the historical citations and the present-day picture is straightforward. There are two separate questions, governed by two separate kinds of document, and a contractor needs the right answer to each.
- How do I verify the enclosure's shielding performance? — IEEE 299 is the measurement standard. It defines how shielding effectiveness is surveyed across frequency, and it is the modern successor to the MIL-STD-285 method.
- How do I build and accredit a secure space? — ICD 705 and its Technical Specifications govern the construction and accreditation of SCIFs, including physical security, acoustic, and where required RF protection. This is the framework that superseded the older NSA construction specs.
- What attenuation must the shield actually deliver? — That comes from the facility's TEMPEST countermeasures determination, not from a generic legacy number. The required shielding effectiveness is set by the threat and zoning analysis for the specific space.
- What if my equipment also has EMC obligations? — Defense electronics tested in the space may carry MIL-STD-461 requirements, which drive their own room features independent of the secure-facility standards.
For a SCIF program, the construction baseline is ICD 705 and the measurement baseline is IEEE 299; the legacy NSA numbers are translated into those current frameworks rather than used directly. Our guide to government and defense shielding for SCIF and TEMPEST secure facilities walks through how these pieces fit together on a real project. Where the work involves a test chamber for defense hardware, our overview of MIL-STD-461 compliance in shielded room design covers the parallel EMC obligations.
Reading a Legacy Specification Correctly
When a statement of work or an inherited drawing references NSA 65-6, NSA 94-106, or MIL-STD-285, do not assume the customer literally wants a withdrawn standard reproduced. In almost every case the intent is a defined level of RF shielding for a secure space, validated by measurement and accepted under the current accreditation framework. The contractor's job is to confirm the real, current basis of acceptance with the accrediting authority or contracting officer, then design and test to that.
This is where experience matters more than the citation. A team that has built secure facilities through the transition from the NSA specs to ICD 705 can read the legacy number, infer the performance the customer needs, and deliver an enclosure that passes the IEEE 299 survey and satisfies the accreditation. National Shielding's secure-facility shielding practice exists to make that translation cleanly, so a forty-year-old spec number does not turn into a rework loop.
Frequently Asked Questions About Shielding Standards
What is the NSA 65-6 shielding standard?
NSA 65-6 was an older National Security Agency specification defining RF shielding construction and performance requirements for secure government facilities and shielded enclosures. It has been superseded; secure-space construction and accreditation are now governed by ICD 705 and current TEMPEST guidance rather than NSA 65-6, which survives mainly as a citation in legacy documentation.
Is MIL-STD-285 still used?
No. MIL-STD-285, issued in 1956 as a method for measuring enclosure shielding attenuation, has been withdrawn. Its test methodology was carried forward and modernized in IEEE 299, which is the standard the industry uses today to measure the shielding effectiveness of electromagnetic enclosures. A legacy reference to MIL-STD-285 should be interpreted as calling for an IEEE 299 survey.
What replaced MIL-STD-285?
IEEE 299 (Standard Method for Measuring the Effectiveness of Electromagnetic Shielding Enclosures) replaced MIL-STD-285 as the recognized measurement standard. Both define how to verify an enclosure's attenuation across frequency rather than how to build it, so IEEE 299 is the direct modern equivalent for shielding-effectiveness acceptance testing.
What is the difference between NSA 65-6 and ICD 705?
NSA 65-6 was a legacy NSA construction and performance specification for shielded secure facilities, while ICD 705 is the current Intelligence Community Directive governing the construction and accreditation of SCIFs. ICD 705 and its Technical Specifications, together with the project's TEMPEST determination, now define what older NSA specs once covered, which is why ICD 705 is the framework contractors build to today.
What is NSA 94-106?
NSA 94-106 was a later National Security Agency specification for shielded enclosures that succeeded earlier documents in the NSA 65-series lineage. Like NSA 65-6, it has been largely overtaken by ICD 705 as the governing accreditation framework. Contractors should treat an NSA 94-106 reference as a legacy citation and confirm the current accreditation basis with the accrediting authority.
Which standard do I build and test a SCIF to today?
A SCIF is built and accredited under ICD 705 and its Technical Specifications, with shielding effectiveness measured per IEEE 299 and the required attenuation set by the facility's TEMPEST countermeasures determination. The older NSA numbers are translated into these current frameworks rather than used directly, so the practical baseline is ICD 705 for construction and IEEE 299 for measurement.
Why do old specifications still reference withdrawn standards?
Standard numbers persist in inherited drawings, renovation specifications, and institutional memory long after the documents are withdrawn or superseded. A facility validated decades ago carries its original citation forward, and specifications often copy prior language. The correct response is to confirm the real current basis of acceptance with the contracting authority and design to that, not to reproduce an obsolete standard.