Remember that the US had started building a 3rd set of locks for the Panama Canal in 1939, so when the Montana & Midway classed were designed, it was expected that they would be able to use the Panama Canal via the new locks!
After the end of the war, the US spent 1945-48 conducting a new study on the Canal, focusing on security and making it attack-resistant, as well as looking at capacity requirements.
While this study eventually supported abandoning the Third Locks project in favor of a new sea-level canal, in 1944-45 it would have been expected by the USN that the project would be resumed and completed after the end of hostilities.:
Interestingly, the current, Chinese-built completed "Third Locks" did use the excavations for the abortive US work.
3rd locks after suspension in 1941, Miraflores:
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And in 1953:
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Here is the under-construction modern set of locks for the same location and the reverse viewpoint:
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And the completed Cocoli Locks:
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