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This is a complex question, especially as it implies two concepts, 1. that the First World War blockade was successful and 2. the attempts to do similar during the Second was not.
The extent to which the First World War blockade was successful is still debated within the historiography. Indeed, the historian Eric Grove presented a paper weeks before his recent death exploring the complexity and complicity of the Norway-Sweden-Netherlands-Britain trade triangle. In general he re-highlighted the well known problem for economic warfare, how does a nation use all its economic and military power to block trade to an enemy without both adversely effecting relations with important neutrals and negatively impacting its own war economy. Grove pointed out how difficult it was for a nation like Britain, that was metaphorically as well as, to a certain extent literally, at the centre of global trade to physically halt trade within an increasingly complex web of finance, insurance, and shippers. Highlighting that British exports were profiting from Swedish-Netherlands trade (that was definitely being sent on to Germany). Was the damage to the German war effort, that halting trade would cause, worth the wider negative impact to British wealth and balance of trade?
So the success of the first blockade was complex and still debated. What is clear from work such as Adam Tooze and Joseph Maiolo was the extent to which the legacy of the blockade had on Nazi (and wider fascist) ideology and economic thinking. This dwelt upon the perceived weakness of relying on a global capitalist system to provide essential resources, and the fragility of modern societies to endure hardships, especially when corrupted by a supposed enemies within (Jews, Socialists, take your pick). This promoted the wider drive for autarchy, coupled with a ‘hardening’ of society and culture to provide a greater degree of resilience for any future conflict. So to a certain extent Germany during the 30s had undertaken domestic and industrial changes specifically to harden its ability to endure future blockade and sanctions. The 4 year economic plan, as well as overt military industrial expansion, was also designed to make Germany less reliant of overseas trade for core and rare resources.
The question also asks for the blockade to be separated out of a wider strategy of economic warfare which most definitely included widescale strategic bombing and covert activities, resistance movements, but also far less sexy approaches. This included bullying neutrals with access to finance and shipping, bulk purchasing raw materials from neutrals and diplomacy. As well as flat out bribery of neutrals. It very difficult to unpick these approaches as they were core to pre war British and French policies and essential to the way Britain “Alone” (Trademarked) was going to conduct the war. Im going to mostly avoid bombing as it’s a huge question in its own right.
Germany, like all of Europe, was broadly a net importer of raw materials and food. David Edgerton, like Tooze, describes the German choice of autarchy and pursuit of ‘substitutes’ and synthetic alternatives as fundamentally a response to this perceived economic weakness. These efforts went someway towards mitigating but not solving a need for significant imports of food, common materials like iron and oil, as well as smaller but crucial materials ranging from chemicals, rare metals, rubber etc. Ironically and tragically the actions taken by Germany in pursuit of autarchy and militarisation eventually prevented the peaceful acquisition of the resources it needed. Basically, Germany chose militarisation and conquest over trade.
The impact of the allied blockade is difficult to unpick from the wide economic crisis being experienced by Germany throughout the conflict. Simply Germany did not have the resources to fight an intercontinental war. Economically and financially it existed hand to mouth. Raw materials, food and labour were insufficient for the scale of warfare it was engaged in.
Like the first world war, the blockade was as much about civilian, legal, financial and trade controls as actual naval interdiction. British finance, insurance and shipping dominated the mechanisms of international trade. The impact of depriving businesses of licenses and credit perhaps more impactive than how to find and interdict ships at sea. This was done jointly via legal and practical approaches to contraband control and the Admiralty led Contraband Control Board, and through wider economic intelligence and controls via the Ministry of Economic Warfare. Shipping controls through the Ministry of Shipping also played an important role as so much of the worlds trade were carried by British and allied shipping, the state controls over this shipping represented a near hegemony over potential shipping available to carry trade to neutral and enemy ports.
A mix of carrot and stick approach towards trade with adversaries were undertaken. Britain attempted to deprive Germany of war materials by pre-emptively purchasing it themselves. This was supported by the ability to influence which traders and shippers got credit and insurance needed to lubricate the mechanics of trade. The introduction of legal certification for trade deemed non contraband required potential traders and shippers to seek authorisation before they even departed ports, domestic or neutral, or risk sanctions. These sanctions included inspections, being deprived of bunkerage, being put on ‘blacklists’ and increased risk of seizure and forfeiture. Once on the sea, trade destined for Europe were directed towards control ports in Scotland and the south coast. Similar control areas were set up at Gibraltar and the entrances to the Gulf, the red sea, the west and east coat of Africa.
Basically British interests had enough control over global money, insurance, port infrastructure and shipping to bully neutral carriers/traders into agreeing to British rules ‘or else’. On a national level Britain had enough diplomatic and economic leverage to persuade neutrals nations to comply – to some extent. The attitudes of the United States for example was a constant source of concern and a difficult balance to strike.
At sea, shipping bound to and from Germany (and later most of Europe) was funnelled through choke points (control zones/ports) for inspections. The treatment given to traders and carriers depended on their trustworthiness in complying with British conditions as well as an ever growing sophistication of trade/shipping intelligence.
I don’t think im going to try and cover all the aspects of the war against German shipping as its too large and actually not well covered by available literature. Like the first world war there were obviously problems, gaps and legal loopholes, but broadly German owned shipping had been effectively swept from the sea, seized by allied powers or held in neutral ports unable or unwilling to sail by the end of 1940. The biggest problem, as is the First World War was neutrals. Until their eventual occupation, the Netherlands, Norway, Yugoslavia were all problems. The views and opinions of the United States ever present looming in the background. Blockade and ‘Belligerent rights’ had been the thorn in GB-US relations for the whole of the 20th century so far. Food was also the great dilemma facing Britain and neutrals. Was food to be contraband? And if so how much should be allowed in on humanitarian grounds.
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As the war progressed and German successes grew the dynamics of the blockade, economic warfare and the German war economy changed. The occupation of France, Belgium, Netherlands, Greece, Yugoslavia, Norway provided huge windfalls of raw materials, money, labour and food. All of which were exploited and provided significant boosts to the troubled German war economy. France contributed a significant proportion of material and money through extractive approaches to occupation costs and import/exports. Basically, Germany charged France for its occupation and ‘bought’ manufactures, raw materials and food with credit that would never be paid back. Denmark and The Netherlands were exploited for their food production. However, despite these huge windfalls and increases in economic base, these occupied territories, like Germany, had resource deficiencies compared to their economic potential and were broadly food deficient. Despite the resources flowing through neutral nations, Germany and occupied territories were still ultimately reliant on a flow of imports that were in the main not forthcoming.
Prior to their occupation, the Dutch were probably the weakest link in the blockade as well as the south eastern European countries. After the widening of the war Sweden, Switzerland, Spain and Portugal and (Vichy) France were the biggest leaks in the blockade system. The big outlier to this system was the USSR. Until the invasion of the USSR the trade between Germany and USSR offset a great deal of this resource deficiency. Flows of metals, oil, chemicals and rare materials flowed into Germany in exchange for machine tools and technologically advanced equipment. As the war waged on and Germany could see little hope in defeating Britain and their increasingly close relationship with the United States, their resource deficiency helped crystallise plans for the invasion of the USSR to seize resources it was otherwise at the mercy of the goodwill of the USSR. Germany needed the resources of the USSR to offset the impact of the blockade. Ironically the invasion ceased the supply of those much needed resources. The blockade and embargo of Germany certainly contributed to the poor long term position of the German economy and promoted the widening of the war to USSR and ultimately the United States.
If this is the case, why did the economic blockade not become more catastrophic for Germany? Primarily because Germany, through its brutal occupation policies was able to diffuse and disperse the impact of blockade and economic warfare amongst a much wider population than during the first. Crudely Germans ate while Poles and Greeks starved to death. German factories ran while French industry remained relatively idle. German armoured vehicles moved while the rest of the continent resorted to horses and bikes, and eventually ate the horses. The people of Europe suffered to spare those of Germany and prolonged its eventual collapse. This is not to suggest that Germans did not suffer, they did also. Rationing of food and resources, as well as tight credit controls were implemented from the outset.
There were certainly gaps in the blockade. Trade continued through Spain and Portugal for example. But even with the constant drip of blockade runners wasnt enough to sustain a long German war effort.
The expansion of the German output into 1944-5 confuses the analysis as observers would naturally expect it to falter, yet Tooze points out that you need to examine changes in Trajectory of production. Perhaps in the days of Covid and R rates people might more easily understand the artificial increasing growth of armament production. What Tooze and Overy highlight is how economic warfare, blockade and bombing flattened this economic trajectory. Without blockade and the combined impact of economic warfare and strategic bombing it is highly likely that the German war economy would have been able to produce much more.
The practical impact of the lack of nearly every economic material are probably too specific for me to explore, yet clearly impacted the strategic choices of Germany as well as operational decision making. You only have to examine the choices Germany made regarding oil at a strategic level (Caucases/Stalingrad) and the operational (Ardennes) to see the impact of German resource limitations on the conduct of the war. The hunger plans of General Plan Ost, the horrific exploitation of slave labour and every other extractive and brutal policy of wartime Germany can be seen as both a result and of German economic weaknesses worsened by allied economic warfare. Blockade and control of the sea was a central aspect to this approach.
I have mostly used:
Edgerton, David. Britain's War Machine. St Ives, United Kingdom: Penguin Books, 2012.
Maiolo, Joseph A. Cry Havoc: The Arms Race and the Second World War 1931-1941. London: John Murray, 2010.
Todman, Daniel. Britain's War: Into Battle, 1937-1941. United Kingdom: Penguin Books, 2017.
Tooze, Adam. The Wages of Destruction. London: Penguin Books, 2006.
Adam Tooze and Jamie Martin. “The economics of the war with Nazi Germany”, in The Cambridge History of the Second World War, Volume 3, Total War: Economy, Society and Culture. Ed Michael Geyer and Adam Tooze, 2015
Ricard Overy. Why the Allies Won. Pimlico Books, 2006.
Mark Mazower. Hitlers Empire. Penguin Books, 2008
Jeffrey Fear. “War of the factories” in The Cambridge History of the Second World War, Volume 3, Total War: Economy, Society and Culture. Ed Michael Geyer and Adam Tooze, 2015
David Edgerton. “Controlling resources: Coal, Iron Ore and oil in the second world war” in The Cambridge History of the Second World War, Volume 3, Total War: Economy, Society and Culture. Ed Michael Geyer and Adam Tooze, 2015
Lizzie Collingham. “The human fuel: Food as global commodity and local scarcity” in The Cambridge History of the Second World War, Volume 3, Total War: Economy, Society and Culture. Ed Michael Geyer and Adam Tooze, 2015
The actual mechanics and history of the naval blockade I have surprisingly struggled to find. This is especially strange given then copious literature on the First World War blockade. Maybe im just looking in the wrong place. But all the “war at sea” style histories of Roskill, Barnett and Mawdsley don’t seem to really cover it. I know there is some “official” HMSO series covering the Blockade especially Mendlicott, but unfortunately I don’t have them. There is one on Amazon right now for £1000 if you have that spare. So I would love to see people adding more on actually how the Control Zones worked in practice and Admiralty prize courts etc.
This is Eric Groves last ever presentation at the Kings College London seminar series on
The Blockade Legend: the Limitations on the British Empire's Blockade of Germany, 1914-1917
https://www.youtube.com/watch?v=ZagFa5p_q7w
Edit. Nicholas Tracy's. Sea power and the Control of trade. From the Naval Historical Record Society is also useful for the setting up of contraband rules and control zones
Andrew Boyds. British Naval Intelligence. Is good for the economic warfare intelligence.
Im not sure on the rules of bulk posting a source extract. But i found this on Imperial War Museum online archives. From an article of 1939. It has a nice (if very sanitary) description of how the blockade was implemented in the first weeks of war off Weymouth control port.
All of the below is quotation (im not sure how to format it correctly in reddit)
From the Imperial War Museum online archives.
https://ww2memories.wordpress.com/2011/09/21/contraband-during-ww2/
One Month’s Seizures
In a typical week, the first week of October 1939, the British Contraband Control detained 25,000 tons of contraband goods consigned to German ports, the cargoes included:
13,800 tons petroleum products
2,500 tons of sulphur
1,500 tons of jute
400 tons of other fibres
1,500 tons of feeding stuffs
1,300 tons of oils and fats
1,200 tons of foodstuffs
600 tons of oilseeds
570 tons of copper
430 tons of other ores and metals
500 tons of phosphates
320 tons of timber
quantities of other commodities were also detailed:
copra
chemicals
cotton
Wool
hides and Skins
rubber
silks
gums and resins
tanning material
ore-crushing machinery