It was a "gap-filler" in the Pinetree Line set up to monitor the skies for aircraft approaching from the north.
ɪt wʌzɐ "ɡˈæpfˈɪlɚ" ɪnðə pˈaɪntɹiː lˈaɪn sˈɛt ˌʌp tə mˈɑːnɪɾɚ ðə skˈaɪz fɔːɹ ˈɛɹkɹæft ɐpɹˈoʊtʃɪŋ fɹʌmðə nˈɔːɹθ.