I want to know the answer to the following question:
What caused the Russians based in Memel to be successful deeper into Prussia?
All the background I'm provided with is that "The Russians then used Memel as a base to invade East Prussia and defeated a smaller Prussian force in the fiercely contested Battle of Gross-Jägersdorf on 30 August 1757.". Is that enough to answer the question?
Answer: yes