Even with the modern plumbing, plumbs and trim tanks. The US subs crash dived in twice the time that the U-boats did ...
. But im comparing VII against Gato/Balao. Maybe a fair comparision would be with the IX. but i dont know it s crash dive time.
Once the tanks were filled with water, they starting pitching down the sub, and it takes some time, the crew reaches the forward edge earlier than the water filled the tanks, and the planes got into position, so i think its an important help for the sub to sink faster. it s true that the crew weight is nothing compared to water s, but with the forward balance of weigth , it pitched down the sub and sinked, just like an airplane, with "inclined speed" more than heavier weight, later the tanks gets filled and the sub can gain depth without the use of speed.