Why pre-war MAC ships could blunt the U-boat campaign

Would purpose-built merchant-aircraft-carrier hybrids work?

Yes, especially if numerous before 1939; small Swordfish groups could protect convoys and suppress surfaced U-boats.

The useful hybrid is a tanker or grain carrier whose cargo handling can coexist with a flight deck, small hangar and about six aircraft. One or two in each convoy would not equal a dedicated escort carrier, but they could provide persistent air presence during the dangerous early war years. Radar-equipped Swordfish would force U-boats underwater and reduce opportunities to develop experienced crews. Because the Atlantic struggle is an attrition contest, slowing German learning in 1941-43 could reduce later merchant losses disproportionately.