Which German research delay would weaken the U-boat threat?

On 11 January 1910, which single German technology would you slow by 50 percent to inhibit the U-boat threat?

Battery technology is the preferred choice in the exchange, with diesel development offered as an alternative that would restrict range and recharging.

Runon's diesel proposal would reduce machinery efficiency, increasing the hull space required and the time spent recharging batteries on the surface. It would also shorten range for a given hull size. Battery development is the competing choice because it affects submerged endurance directly. Alex adds that earlier batteries produced especially dangerous gases, so delaying improvement could also increase the danger to crews. The alternatives therefore affect different parts of submarine operation: surface running and recharging, or underwater endurance and battery safety.