The first example flew at Eastleigh aerodrome, Southampton, on April 25, 1938, bearing the Supermarine 'Class B' marking N-15, and later made a catapult launch from the brand-new Argentine light cruiser ARA La Argentina in Morecambe Bay, Lancashire. By October 15, 1938, the Walrus had received the code M-O-9 and on January 3, 1939, M-O-9 was ferried to Barrow-in-Furness where ARA La Argentina was anchored.
The second Walrus, bearing the 'Class B' marking N-16, first flew at Eastleigh on April 29, 1938, and, following acceptance flights, was coded M-O-10 and loaded aboard ARA La Argentina on January 5, 1938. The two Walruses were assigned to the Escuadrilla de Observación de Aviación de la Escuadra de Mar and became operational in the autumn of 1939.
On October 2, 1945 negotiations began with Vickers-Armstrong for an additional batch of Walruses and eventually eight ex-RAF Supermarine Type 236 aircraft were chosen. The selected aircraft included X9564, X9571, X9573, Z1758, HD823 plus three unidentified examples. (Some of these Walruses were Walrus Mk.IIs but Aviación Naval records refer to all eight examples as Mk.Is.)
Following overhaul and test flights at Hamble (bearing the Supermarine 'Class B' markings N-33 to N-40 in an unknown sequence), the Walruses were painted in Aviación Naval's standard two-tone grey scheme and received the codes 2-O-23 to 2-O-30, and the first two were delivered on October 9, 1946.
The ten aircraft are listed below by their first allocated code, followed by codes allocated in sequence for that particular aircraft. Quoted in brackets are the test flight 'Class B' markings. Abbreviations: TOC - taken on charge, SOC - struck off charge.
M-O-9, M-O-1, 2-O-10, 2-O-12. TOC 1939, SOC 1947 (N-15)
M-O-10, M-O-2, 2-O-11, 2-O-13. TOC 1939, SOC 1949 (N-16)
2-O-23, M-O-2, 7-O-1. TOC 1946, SOC 1957 (N-33)
2-O-24, M-O-3. TOC 1946, SOC 1952 (N-34)
2-O-25, M-O-4, 7-O-2. TOC August 28, 1947, SOC 1953 (N-35)
2-O-26, M-O-5, 7-O-3. TOC November 3, 1947, SOC 1958 (N-36)
2-O-27, M-O-5, 7-O-4. TOC August 28, 1947, SOC 1953 (N-37)
2-O-28, M-O-7. TOC November 3,1947, SOC 1953 (N-38)
2-O-29, M-O-8, 7-O-6. TOC February 13, 1948, SOC 1958 (N-39)
2-O-30, M-O-9. TOC February 13, 1948, SOC 1952 (N-40)
Remarks by Georg v. Rauch: "The Walrus had a nasty habit of leaking hot oil into the cockpit. They were only purchased because they were lighter than the far more reliable Grumman J2F."