I tried it first, but it not work for me:
var mouse_dir = (get_global_mouse_position() - $Tank_gun.global_position).normalized()
var corrent_dir = Vector2(-1, 0).rotated($Tank_gun.global_rotation)
$Tank_gun.global_rotation = corrent_dir.linear_interpolate(-mouse_dir, 50 * delta).angle()
Use in _physics_process