I don't know if it was some sort of master plan but I doubt it. However the chips fell, Marvel, then called Timely has two of the most famous and successful Golden Age comic book superheros in the Human Torch (who wasn't "Human") and the Sub-Mariner (who wasn't always a "hero"). Now in this new series of trades dubbed "Decades" we get a nifty batch of Subby's and Torch's earliest squabbles.
The idea that they existed in the same universe likely rocked the world of more than a few fans at the time. We are so used to expansive and elaborate continuities these days that the raucous early days of comics have a refreshing atmosphere of pure creation. Eventually the two would become partners alongside Captain America, the Whizzer and Miss America as part of the All-Winners Squad, but in these early encounters they'd rather fight than switch. Almost all the work here is by the two creators of these characters -- Bill Everett and Carl Burgos, although there is one story drawn by the infamous "Unknown". This one is sheer fun.
Here are the covers of the comics in the collection, though of course only the Sub-Mariner and Torch material is included.