Recently a German populist said (in context of Frontex effectiveness) that during the first world war the Royal navy managed to completely blockade Germany and not one ship slipped through. He also mentioned that they had no radar and until 1916 no aerial reconnaissance.
How accurate is this statement? I know submarines were able to get around the blockade and some auxiliaries and merchant raiders broke through. Also airships were used for reconnaissance. So how effective was the blockade and how was this achieved?
So when you think about the blockade dont think about British ships sitting right off German harbors in the Jade and Elb estuaries.
Britain opted for a "Distant Blockade" where she would seal off the Scotland to Norway gap in the North Sea and the English Channel.
That meant she just had to have ships controlling what ships entered those routes. And that due to mines and coastal forces German forces did have some degree of freedom of movement n the North and Baltic Seas. That is how you have Uboats head out on patrol and the High Seas Fleet even shelling towns on the English Coast.
The big problem that also faced the RN was that of Neutral Shipping, Norwegian, Danish, and Dutch along with US and many other nationally flagged ships still had rights to trade with nations inside that blockade zone, though certain war goods or goods which would then be sold to Germany were out. And the RN had continuous problems and protests over their enforcement of the blockade on neutrals.
But yes German flagged merchant shipping was virtually scoured from the seas by the end of 1914. Many ships raced to or never left large neutral ports like New York as they knew it to be pointless, they were not going to make it back to a friendly port.
It was also from their ships already at sea that 99% of Germany's surface raiders, either real warships stationed overseas, or converted merchantmen came from, they were specifically over seas so they WOULDNT be caught by the blockade.