You can use Polygon for that and define the body manually. It might look like the following, starting at the bottom left vertex and going clock-wise until bottom right. You can of course change those values and adjust it to your sprite.
float[] vertices = new float[] {
-2, -2,
-2, 2,
-0.5f, 2,
-0.5f, 3,
0.5f, 3,
0.5f, 2,
2, 2,
2, -2
};
Polygon submarine = new Polygon();
submarine.setVertices(vertices);
Now you can rotate this polygon, just like the sprite, and move it and scale it. Just make sure you keep the polygon and your sprite synchronized. For collisions you can use Intersector.
For debugging of the polygon you can use a ShapeRenderer to render it on your screen.
shapeRenderer.begin();
shapeRenderer.polygon(polygon.getTransformedVertices());
shapeRenderer.end();