Why postwar Truman policy would not abolish American sea power

Would a Truman administration have gutted the US military and Navy?

No; he expects a large force with possible reductions, not disbandment or an all-nuclear strategy.

A somewhat smaller postwar force would still be far from wholesale disarmament. Defence spending remained a major tool for employment and infrastructure, while legislation and institutions limited a president's ability to abolish the Navy or Coast Guard. Larger reserve forces could also offset some reductions in active divisions. Truman's horror at nuclear use makes an exclusively nuclear defence posture especially implausible. The counterfactual must account for institutional power, congressional politics, reserves, and the president's own outlook.