GUPPY refits as a bridge to postwar submarines

Did GUPPY refits overstretch wartime submarine hulls and represent a wrong US Navy decision?

No; they were a necessary bridge that kept the force viable until industry could deliver mature postwar submarines.

GUPPY refits are defended as a necessary way to keep wartime submarines viable until replacements enter service. The answer does not accept the question's conclusion that adding equipment and batteries made the program a mistake. Moving from late-war technology to the first postwar generation is described as manageable, while the following generation demands a much larger advance. Retaining upgraded older boats gives the industrial base time to develop and produce that second postwar generation.