Thanks guys for the support and opinions.
I dont think there's right or wrong decision here. You just have to go by the situation at hand. I would have probably engaged the BB if I had been able to get any closer.
With 4 torpedoes and noway to get closer than 6500m of the BB I thought I had a better chance to sink the tankers.
And since this would have not been my first BB sunk it was easier to let it go.
Where are those big aircraft carriers?
Anyway the crew is happy that we're heading home and most importantly everyone's still alive and well