However, Scheer seems to have quickly realised that further battles with a similar rate of attrition would exhaust the High Seas Fleet long before they reduced the Grand Fleet. Further, after the 19 August advance was nearly intercepted by the Grand Fleet, he no longer believed that it would be possible to trap a single squadron of Royal Navy warships without having the Grand Fleet intervene before he could return to port. Therefore, the High Seas Fleet abandoned its forays into the North Sea and turned its attention to the Baltic for most of 1917 whilst Scheer switched tactics against Britain to unrestricted submarine warfare in the Atlantic.