The Moscow Signal

Summary

From 1953 to 1976 Soviet transmitters aimed low-power microwave beams at the American embassy in Moscow. A 1978 health study found no harm to its staff.

Where the beams came from was established: buildings about 100 metres away. The levels were measured, and they were low. Why the Soviet Union sent them has not been disclosed, and that part of the case remains open.

What is documented

The beams. From 1953, beams of microwaves at 2.5 to 4.0 gigahertz were aimed at the embassy's central building. Until May 1975 they came from a Soviet apartment building about 100 metres to the west and struck the west facade, most strongly between the third and eighth floors. The power density reached up to 5 microwatts per square centimetre for about nine hours a day. The average in the exposed rooms is estimated at 1.5.

1975. From May 1975 two beams arrived instead, from buildings about 100 metres to the east and to the south. They reached up to 15 microwatts per square centimetre for 18 hours a day, with averages of 1.3 to 3.3. The highest reading recorded was 24, close to a window in a tenth-floor room, for a period of two hours.

The screens. On 6 February 1976 screening was installed on the windows. With reductions in the transmitters' power, it brought the level in even directly exposed rooms below 0.1 microwatts per square centimetre.

How strong that was. In 1998 the International Commission on Non-Ionizing Radiation Protection (ICNIRP) set a reference level for public exposure at frequencies from 2 to 300 gigahertz of 10 watts per square metre, which is 1,000 microwatts per square centimetre. The highest reading at the embassy was 2.4 per cent of that figure. J. Mark Elwood, reviewing the case in 2012, described the exposures as low, but similar to or greater than present-day exposures from sources such as mobile phone base stations.

The study. In 1976 the Department of State commissioned a study of the health of embassy staff and their families from Abraham Lilienfeld and colleagues in the Department of Epidemiology at Johns Hopkins University. It compared 1,827 employees who had served in Moscow between 1 January 1953 and 30 June 1976 with 2,561 who had served only at other posts in Eastern Europe (Belgrade, Bucharest, Budapest, Leningrad, Prague, Sofia, Warsaw and Zagreb), and identified 2,819 adult dependents and 5,474 children. The sources were medical records, questionnaires and death certificates.

The finding. The report, completed in 1978 and running to 447 pages, concluded that, "with very few exceptions", an exhaustive comparison of those who had served in Moscow with those at the other posts "revealed no differences in health status as indicated by their mortality experience and a variety of morbidity measures". As of Elwood's review in 2012, it had never been published in the peer-reviewed literature.

The purpose. Herbert Pollack, professor emeritus of clinical medicine at George Washington University and the State Department's contract officer, wrote in 1979 that the purpose of the beams was unknown. Elwood's 2012 review gives no later explanation, and the registry has found no official statement of purpose from either government.

The dissent. John Goldsmith argued in the 1990s that the comparison posts had also been exposed to microwaves. In his reading, all cancers among employees and dependents at Moscow and the other posts combined numbered 116, against 80.5 expected. He also claimed that exposure data and some cancer cases had been withheld from Lilienfeld's team. Elwood found "no direct evidence" for Goldsmith's position and concluded: "The conclusions of the original report are supported."

Leading explanations

A deliberate Soviet microwave transmission. Established. The beams were measured over two decades, their frequencies and power recorded, and their sources located in buildings about 100 metres away. They fell to almost nothing in 1976, when screens went up on the windows and the transmitters' power was reduced.

Harm to health. Not supported. The 1978 study found no difference in mortality or illness between Moscow staff and staff at other Eastern European posts. Its validity rests on the other posts not having been exposed to similar radiation, and that assumption is the one Goldsmith challenged. Elwood's review found his reanalysis unsupported by direct evidence and the original conclusions sound.

The purpose. Not established. Pollack wrote in 1979 that it was unknown, and no purpose has been officially disclosed since. The registry does not supply one.

Current status

Partially explained. What the Moscow Signal was is settled: microwave beams from Soviet transmitters in nearby buildings, measured and located. Whether it harmed the people inside has been studied, and the study found no harm; its main critic's reanalysis was found unsupported in Elwood's 2012 review. Why it was sent remains undisclosed. The registry would change the status on the release of records, American or Russian, that state the purpose.

The case invites comparison with the Havana incidents reported from 2016 (AR-0045). The difference is in the record. In Moscow the beams were measured for more than twenty years and their sources were found. In the Havana cases, no weapon has been shown to have caused any incident.

Last reviewed: September 2026. Records are provisional. Where the evidence changes, the entry changes. Found an error? Tell us.