I tried to sink the Warspite on my first LSH3 patrol. Suffering from my torpedo malfunctions, I finally managed to score three hits on her after reloading my save (very often). She capsized, sank to the ground, but I got no sinking confirmation. I did encounter various destroyers, but managed to escape. It felt as difficult as (stock) SH5.
In shallow waters, you are supposed to hit the battleship below the turrets, triggering secondary explosions. Worked well in SH4 and SH5, but I did not manage to do so in LSH3.
Best,
Brett
p.s.:
I then sank the Illustrious instead

. Two torps were enough to break her up.