What should I do for the 150k damage mission?

Baltimore can get there, though 150k is a big game in a cruiser. Try to stay alive long enough to keep firing: use cover, avoid pushing into several enemies at once, and look for chances to shoot at distracted ships. Use AP on broadside cruisers, and HE when targets are angled or are battleships you can’t reliably penetrate.

If you have another ship with more reliable sustained damage, that might make the mission less of a slog. But with Baltimore, focus on staying in the match and picking useful shots rather than forcing damage early. A long, steady game gives you more chances to add damage than an aggressive opening that gets you sunk.