[1][2] A conventional design for World War I, the M.18 was a biplane flying boat with unstaggered wings of unequal span braced by Warren truss-style struts.

The engine was mounted pusher-fashion in the interplane gap, and the pilot and observer sat in side-by-side open cockpits.

[3] Six of the 20 machines purchased by Spain remained in service at the outbreak of the Spanish Civil War and were used to attack Nationalist forces on Majorca as well as flying reconnaissance patrols.

[1][2] The first of these, the M.18 Economico ("Commercial"), was generally similar to the military version, but was followed by the M.18 Lusso ("Luxury") which featured an enclosed cabin.

[2] Some 70 civil examples were produced in all,[1][2] some being purchased by joyriding firms such as Ad Astra Aero in Switzerland and some others being used by SISA for training flying boat pilots for airline service in the Adriatic.