Federal Signal Thunderbolt series - Civil Defense Sirens Wiki2022-08-24
The Thunderbolt 1000T became the standard model of Thunderbolt in 1954, with the Thunderbolt 1000 becoming optional. The Thunderbolt 1000T was intended for civil defense purposes, while the Thunderbolt 1000 was switched to being used for other purposes, though it could still be used as a civil defense siren if necessary. A Thunderbolt 1003.
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