I got to fight [the Doomsday Machine] today
What a coincidence, I did that mission earlier today as well on my Science Lt Commander character.
My first character, a Tactical Captain, flew a Heavy Cruiser when he was a Commander. I'm pretty sure I'm going with the Excelsior
instead of the Research Vessel for my Science Captain.
Fair warning the ship plak you get as part of your promotion won't cover the Excelsior you have to use energy credits to buy it and it costs 137,000 so save up.