685 or 686 possible ?
(see also many others with designation 'frontier' in the following list)
https://www.mobileradar.org/army_units_600_2691.html
685th Signal Aircraft Warning Company (Special)
Activated: 9 June 1942, as 685th
Signal Aircraft Warning Reporting Company, Special, at Drew Field, Tampa, Florida
Redesignated: 5 September 1942, as 685th Signal Aircraft Warning Company (Special)
Relocated: Newfoundland Base Command
Relocated: Plant Park, Tampa, Florida
Relocated: 1 March 1945, Drew Field, Tampa, Florida, to await disbandment orders
Disbanded: 6 July 1945
686th Signal Aircraft Warning Company
Activated: 9 June 1942, as 686th Signal Aircraft Warning Company, Special, Drew Field, Tampa, Florida
Redesignated: 16 September 1942, as 686th Signal Aircraft Warning Company, Special
Relocated: Hato Field, Curacao, Netherlands, Antellies
Subordinate to: Antellies Air Command, Serving in the British West Indies and Netherlands, West Indies
Note: Hato Field was located on the island of Guracao in the Caribbean within sight of the Venezuelan shoreline
Disbanded: 15 December 1944