its stead, only those ships fast enough to make the journey from Zonguldak to Constantinople in a single night were permitted; outside the Bosphorus they would be met by torpedo boats to defend them against the lurking submarines. By the end of the summer, the completion of two new Russian dreadnought battleships, and , further curtailed s activities. 1916–1917 Admiral Souchon sent Yavuz to Zonguldak on 8 January to protect an approaching empty collier from Russian destroyers in the area, but the Russians sank the transport ship before Yavuz arrived. On the return trip to the Bosphorus, Yavuz encountered Imperatritsa Ekaterina. The two ships engaged in a brief artillery duel, beginning at a range of 18,500 meters. Yavuz turned to the southwest, and in the first four minutes of the engagement, fired five salvos from her main guns. Neither ship scored any hits, though shell splinters from near misses struck Yavuz. This was the only battle between dreadnoughts on the Black Sea to ever occur. Though nominally much faster than Imperatritsa Ekaterina, the Turkish battlecruiser's bottom was badly fouled and her propeller shafts were in poor condition. This made it difficult for Yavuz to escape from the powerful Russian battleship, which was reported to have reached . Russian forces were making significant gains into Ottoman territory during the Caucasus Campaign. In an attempt to prevent further advances by the Russian army, Yavuz rushed 429 officers and men, a mountain artillery battery, machine gun and aviation units, 1,000 rifles, and 300 cases of munitions to Trebizond on 4 February. On 4 March, the Russian navy landed a detachment of some 2,100 men, along with mountain guns and horses, on either side of the port of Atina. The Turks were caught by surprise and forced to evacuate. Another landing took place at Kavata Bay, some 5 miles east of Trebizond, in June. In late June, the Turks counterattacked and penetrated around 20 miles into the Russian lines. Yavuz and Midilli conducted a series of coastal operations to support the Turkish attacks. On 4 July, Yavuz shelled the port of Tuapse, where she sank a steamer and a motor schooner. The Turkish ships sailed northward to circle back behind the Russians before the two Russian dreadnoughts left Sevastopol to try to attack them. They then returned to the Bosphorus, where Yavuz was docked for repairs to her propeller shafts until September. The coal