G3M air threat versus cruiser interdiction

Would G3M torpedo bombers make Town-class cruiser operations impossible?

No: early 1939 aircraft numbers were limited, and commerce interdiction could be conducted beyond their effective reach.

The early-1939 Mitsubishi G3M inventory was much smaller than the 204 aircraft available by 1941. A later wartime total cannot be treated as an opening-day force two years earlier. Town-class cruisers could also choose interception areas beyond the bombers' useful coverage rather than loiter near Japanese bases. They could seize merchantmen and place prize crews aboard instead of sinking every target in exposed waters. Range, timing, and commerce-law practice could therefore counter a dangerous aircraft without making the cruisers invulnerable.