The Bars-class submarines were ordered by the Imperial Russian Navy under their 1912 construction programme. 24 boats were ordered; 12 for the Baltic Fleet, six for the Black Sea, and six for the Siberian flotilla. The Black Sea units were built at Nikolayev. These boats were designed by Ivan Bubnov and based on the preceding Morzh class. They were single-hulled, but like the Morzh boats lacked internal bulkheads.

As designed the boats were to have two 900 horsepower electric and two diesel engines. The Black Sea boats had one 75 mm and one 37 mm gun. The torpedo armament comprised four internal 18-inch torpedo tubes and eight external torpedoes in drop collars mounted in recessed niches low in the hull.

The design had numerous shortcomings, including a lack of internal bulkheads and a slow diving time. Surviving boats were modernized after the Russian Civil War by installing bulkheads, new diesels, pumps and extra torpedo tubes (the external drop collars were removed).

Submarine Gagara was laid down on 29 August 1915 at the Nikolaev Naval shipyard in October 1915 and launched on 24 September 1916, commissioned on 20 June 1917.

Seized by the Germans in Sevastopol on 01 May 1918 as US-4. Scuttled on 26 April 1919 near Sevastopol.