Final answer:
The tactic used by Germany to disrupt the British food supply was U-boat attacks. Germany's submarines known as U-boats targeted and sank merchant ships around Great Britain, violating international law. The sinking of the RMS Lusitania by a U-boat had significant implications for the United States' entry into World War I. The correct option is 1.
Step-by-step explanation:
The warfare tactic used by Germany against the British to block the selling and transporting of food during World War I was U-boat attacks. The German navy declared the waters around Great Britain as a war zone, and utilized their submarines, known as unterseeboots or U-boats, to sink merchant ships which they suspected of carrying contraband to the British.
This not only targeted military ships but also attacked neutral and civilian vessels without warning, directly violating international laws of maritime warfare. Notable among these attacks was the sinking of the RMS Lusitania in 1915, which claimed almost 1,200 lives, including American citizens, thereby influencing the United States' stance on entering the war.
These U-boat offensives were part of a larger strategy by Germany to counteract the British-led naval blockade, which was severely limiting Germany's import of essential goods, including food. The strategy to employ U-boat wolf packs in the Atlantic Ocean during World War II, specifically after the U.S entered the war, was also a continuation of the tactic to disrupt the supply chains to the Allies.
This naval campaign eventually faced setbacks due to improvements in Allied tactics and technology, such as the Ultra intelligence from British codebreakers and the establishment of a convoy system.