It was not built to retrieve Soviet satellites, despite an uncited claim in Wikipedia to the contrary. In fact, it probably couldn't. If nothing else, it'd be hard to fit a satellite designed for a different launch fairing into the payload bay of the shuttle and secure it well enough to be able to land with it. The shuttle was designed to bring cargo back, but only satellites that were specifically designed for this purpose.

What the Shuttle was designed to do in a military context is launch into a polar orbit from the coast of California, release a stealthy spy satellite, and return to Earth immediately after during the very same orbit (so about 90min from launch to landing). It therefore needed the very large wings to be able to glide back to Edwards Air Force Base in southern California, which would have rotated up to 1,500km away from the path of the orbiter. And because of the Pacific ocean, there'd be other landing sites available. This cross-range capability impacted every aspect of the design.

The idea was that big rockets which launch satellites are very easy to track, so it was hard to get a bird up without the enemy knowing its orbital path, and if the enemy knew the orbit they could evade overhead passes. So do a surprise launch on the shuttle, do a little orbit maneuvering while you are up there to maximize the enemy's uncertainty over its orbital plane, then immediately let go and land the shuttle--because otherwise they'd know where it was from tracking the shuttle.

I'm not sure if it was ever used this way, and the requirement is now obsolete anyway. You really can't hide a satellite from modern instruments, which have full global coverage, and its critical that orbits are known to avoid collisions in the much more crowded space up there.