Conflict drives technology. RADAR was developed to extend the range of detection for incoming hostile aircraft in WWII. It gives an edge to be able to find planes beyond the limits of human sight and hearing. The Cold War really took the battle underwater as anyone who has seen The Hunt for Red October will verify. In the 1960s, the US developed SOSUS sound surveillance system: a series of static oceanic listening posts to detect the movement of Soviet nuclear submarines. Thousands of hours of tonks, clangs, purrs and rumbles were recorded and sent back to the US for analysis. They picked up a lot of other sounds including the super-low pitched whurps and wwwwls of whale-song.
listen at 10x speed so our ears can up-pick , the Woods Hole people detected a single caller from the Pacific Ocean at 52 Hz - listen here. The latter was captured by Bill Watkins, who tracked and tricked with the high-pitched caller for the last 20 years of his life. "high-pitched" is relative, of course. For comparison fit young humans can detect sounds over 3 orders of magnitude - 20 Hz to 20,000 Hz. Although it is probably fair to say that they can't distinguish pitches at the extremes of the range. You probably get more sensation through your feet or buttocks than your ears for really low pitched sound.
The 52Hz whale caught the imagination of the chattering classes and the Daily Mail & the BBC, who called 'him' the loneliest whale in the world - romantically searching for conspecifics of the opposite sex but never getting off with anybody. There is no evidence for this tale of unrequited love. For all we knew he was a sensation with the ladies and fathered dozens of whale-spawn - who none of them inherited the call sign of dear old Dad. It was suggested that he might be deaf and was thus unable to pitch his song at normal levels. It is known that whales change their tune to suit local style, presumably because females are choosy but normative.
B musculus vs B physalus and see [comparative karyotypes L]. The chromosomes are photographed as a splat down the microscope and each one is cut out [with scissors in the old days] and reassembled in blocks: metacentrics with the centromere [waist] in the middle, telocentrics with the centromere at the end and for pedantic niceness sub-metas and sub-telos for those chromosomes that between the two extreme states. Both pictures were assembled by Ulfur Arnason albeit at 40 years separation in time, but they are 'different' wrt the split between metacentrics 8 or 7 and sub-metacentrics 6 or 7. I don't believe it. Or rather I think they have essentially the same chromosome count and maternal B musculus and paternal B physalus will be well able to line up neatly in the hybrid when it comes to making sperm and egg. Phew! I'm glad that's sorted. If you have an reproductive, fertility or socialisation problems yourself; Uncle Bob will give you a helpful answer without getting up off the sofa.