Modernized submarines in 1941 improve endurance but remain visible

How would GUPPY-standard submarines affect Allied submarine and anti-submarine warfare if sent back to 1941?

They would extend patrols and improve underwater survival, particularly in the Pacific, but would not eliminate aerial-detection risks.

The answer treats improved underwater performance as operationally valuable rather than decisive. GUPPY-standard or equivalent British boats could remain on patrol longer and dive deeper than their 1941 counterparts. Those qualities would especially help crews survive across the wide spaces of the Pacific and Mediterranean. The streamlined boats would still face an important visibility problem from the air, so better submerged performance would not erase Allied or Axis reconnaissance threats.