Problem: the JT3C is a horribly anemic engine, especially the early versions used on the A-E (producing a mere 44.5 kN per engine on the B-52A, increasing only to 46.7 kN/engine on the B-E models). The engines used on the F and G did better, but still topped out at 61.2 kN each. Due to this low engine thrust, the A through G models of the B-52 all required the use of water injection (with the associated weight and space penalties) to augment their engines' thrust for takeoff, without which the aircraft would have been incapable of becoming airborne.
For this reason, the other major users of the JT3C (the 707 and DC-8 airliners) promptly switched over to the more powerful JT4A turbojet when it (the JT4A) came on the market; the JT4A provided up to 77.8 kN of thrust, allowing the JT4A-engined versions of these aircraft to do away with the heavy and complicated water-injection system.
In contrast, the B-52 never switched over to the JT4A, even though, as a heavy bomber aircraft stuffed to the gills with fuel and ordnance, it would have benefited even more from the added engine power than the airliners did.
Why did the B-52 stick to the JT3C (until they finally jumped ship for the JT3D), and not go for the JT4A when it became available?