The main work of the wartime period is the comic opera Der Arzt der Sobeide ('Sobeide's Doctor'), to a libretto by Fritz Zoref. It dates from the years of active service (winter 1917-18), when Gál was supposed to be building a mountain railway with a construction detachment in the Carpathians. It was finished later in Italy and brought safely home - as the only war trophy. It was published in 1919 as his Opus 4, and had a successful premiere in the Breslau theatre on 2nd November of that year, under the baton of Julius Prüwer.

Waldstein characterises this opera, which is set in 16th century Christian-Moorish Granada, as "a cloak and dagger piece with a hint of the poetic from the Arabian Nights" and lists some of the attractions of such material for the composer:

"for Gál it may have been the joyous mood, the liveliness of the situations and no doubt also the local colour that was decisive, the stimulus for direct lyricism, fandango rhythms, the graceful mixture of southern sensuality and ironic heroism". [Wilhelm Waldstein: Hans Gál: eine Studie. Vienna: Elisabeth Lafite, 1965. p. 22.]

The opera has some features which are characteristic of Gál's later stage-works, too: the purely vocal parts are lightly orchestrated, allowing the voices to come through, but the composer gives himself freer rein in orchestral intermezzi, which can be - and indeed were - played independently. It is also, like his last opera Die Beiden Klaas, a 'numbers' opera, consisting of a series of individual pieces. The melodic lines are developed freely, with many interpolations.

The premiere brought the young Gál the highest recognition. The following example gives a representative impression of the reception at the time:

"Here all the virtues are combined which reveal the master of his craft. A lavish richness of melodic ideas permeates the whole work, naturally underlining and enhancing the lyrical episodes with special emphasis, carried along by a harmonic freedom which, in spite of all its boldness appears completely unforced. The sense of a vitalising rhythm, preventing the occurrence of any dead moments, is particularly successfully developed. Behind the natural flow of the parts, especially the singable vocal lines, is concealed a deceptively easy, mature, technical artistry . . .." [Georg Jensch: Volkswacht]