And, for the hackers, here's a version of the Defender ROM, modified by a programmer named Jim Bowley, to render an impossibly difficult version of the game: https://www.youtube.com/watch?v=LhZlOwEvd5M
The above is running on JROK -- http://www.jrok.com/ -- custom silicon to emulate the original chip (much better than MAME), it's contained in an original cabinet, with an original monitor, and a custom built control panel, designed to be as authentic to the original as possible, and hand-built by Jim Bowley https://www.jbgaming.co.uk .
Here's a player, mikeville66, whose video inspired me to get better. This is maximum difficulty on the first-run ROM chips, the infamous Green ROMs: https://www.youtube.com/watch?v=yrkx6vuiMrE
And if you're interested in an instructional video of how to play: https://www.youtube.com/watch?v=8PEpDMgR9D0
Defender was a big game back in the day, grossing about a billion dollars worldwide.