Yes. But these do generate lift. This is basically an underwater glider[1]. It can change it's buoyancy which would make it sink/raise straight down/up. It uses then its wings to turn this vertical speed into horizontal propulsion. It basically flies underwater in a sawtooth pattern (when seen in a side view).

This is a very energy efficient way to go the distance. These machines can loiter for months on a single charge typically. They only need to spend energy on the top and bottom points of their vertical swoops to change their buoyancy.

1: https://en.wikipedia.org/wiki/Underwater_glider