1) Yep, the crew goes for a swim when it runs out of gas.
2) VLAD buoys are not for any particular detection purpose, just like any sonobuoy, but they have certain advantages in certain situations.
VLAD buoys are used more for "blue water" scenarios, as their sensors deploy much deeper (600ft shallow/1200ft deep) than DIFAR buoys (90ft shallow/400ft deep). They are also slightly more sensitive than DIFAR, if my memory serves me correctly. The deeper depths for the sensors allow them to find targets potentially underneath the thermal layer, which can often be deeper than 400 feet.
DICASS buoys have an active sonar mode as well as a passive mode. Their sensors deploy very shallow (90ft) and very deep (800ft), but, I think, are the least sensitive buoys of the three you can deploy.
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