Gap Filler Detail

1961 – National Archives of Canada

Appendix "A" to
S10-136-80/5 TD1279 (DCEC)

GAP FILLER RADAR PROGRAM
REVIEW OF CHANGES IN OPERATIONAL REQUIREMENTS

The orgininal gap filler radar coverage planned for the North Eastern area of North America was based on a low level coverage minimum of 2000 feet. In an attack on this vital area, the concept of defence in depth is valid at all levels of attack. Hence the ability to bring ever increasing pressure of weapons as the raid penetrates deeper into the area at low level, depends directly on the continuity of low level radar coverage. Also the problem of timely identification at low level makes solid coverage throughout the vital area critically important. Based on this coverage criterion, but influenced by the limited USAF funds available for Gap Fillers, a requirement was stated (prior to actual siting) for a total of 45 gap filler sites. This stated requirement was promulgated in the Joint USAF/RCAF CADIN Document Issue 1 Jul 1959 and reaffirmed in Issue 2 May 1961.

In the interim, reassessment of the low level manned bomber threat (1960) indicated the necessity to extend our low level radar coverage down to a minimum of 500 feet above flyable terrain wherever possible, within the perimeter of the vital northeast area. Based on this 500 ft criterion, a new resiting study project was undertaken within the limitations of 45 gap fillers. In order to obtain reasonably solid coverage, it was found necessary to redefine the boundaries of the vital area, and resiting aimed at maximum coverage for this area using 45 gap fillers was carried out.

The boundaries decided on were approximately from latitude 49º 30' N to the US border, and from just east of Manitoba/Ontario border to Nova Scotia. The northern limit had previously been a scalloped line of 230 NM arcs North of the Bomarc Bases. Concurrent with this change in the Gap Filler program FD radars were approved for certain CADIN sites. These new radars, because of their low level coverage characteristics, led to certain overlapping coverage with the previously sited Gap Fillers.

Hence the resiting of sixteen Gap Fillers was necessitated by three main factors:

  1. Some of the previously sited Gap Fillers would now overlap the improved coverage of the new FD radars.

  2. Certain previously sited gap fillers fell outside the reduced borders of the critical area.

  3. Several sites had to be redeployed to fill the enlarged gaps created by more stringent 500 ft coverage criterion.