The German U-boat campaign tries to reduce British trade, while Britain's blockade aims to isolate Germany much more completely. The stronger maritime power can use geography and worldwide naval presence to control routes far from the main theatre. Older British warships near South Africa or India can invoke cruiser rules to stop neutral merchantmen, search for war material, and confiscate or purchase it. The later interception of Asama Maru off Japan gives another example of stop-and-search backed by maritime precedent. Supplies that never reach Germany cannot sustain its war effort.
Chapter · 36:10-39:16
Blockade and U-boats pursue economic war by different means
The First World War contrasts Germany's attempt to interdict British trade with Britain's wider ability to isolate Germany through blockade and global stop-and-search.