I have read one brief account of military planning around the time of Roman emperor Constantine the Great (272 – 337) whereby the Roman navy's rowers could have been substituted by animals (source citation: Anon. de rebus bell. 17,1 – 2).
Do we know anything more about what animals would have been employed, what the proposed scheme was, and whether something along such lines was ever tried in war? The account mentions that the overall aim was to reduce labor cost.
UPDATE I guess I better add more details about my sources before everybody starts thinking this is some kind of joke :) The brief account occurs on p. 365 of German historian Raimund Schulz' book Feldherren, Krieger und Strategen: Krieg in der Antike von Achill bis Attila. There's a footnote pointing to the aforementioned primary Latin source as well as to this French book as secondary source: M. Reddé: Mare nostrum. Les infrastructures, le dispositif et l'histoire de la marine militaire sous l'empire romain.
And the history of warfare has known some strange war vessels indeed, such as the planned World War II air craft carrier made of pykrete (a mixture of wood pulp and ice) ...