Guam was probably logistically involved as a staging base for US/NATO aid going to China to some extent (how significant probably relating to what the US/Filipino relationship looked like in any given T2K timeline -- if Subic Bay and Clark AFB were still in operation it might change things).
Shutting it down to neutralize that aid (or at least complicate it) to the PRC would be a pretty big objective during the war, though once the war goes nuclear and the megatonnage lollapalooza starts erasing most of the Chinese Army, it may have dropped down in priority.
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