During the War to end all wars as it was known at the time Germany was practically landlocked due to the Royal navy not letting any supply though and inland surrounded on both sides by the French and the Russians. (Although the Netherlands kept its trade relations, almost all over neighbors cut ties with Germany due to the invasion of neutral Belgium.) In such situations with most of the labor force in the front lines, the production of food suffered greatly, forcing Germans to find an alternative source of food. Thus the ‘Steckrübenwinter’ (Turnip Winter) had started and Germans would find themselves eating one thing and one thing only. Turnip. Specifically, Rutabaga. And in such circumstances, the dreaded ‘kriegsbrot’ (Warbread) was born. A thing that tastes as bland as it looks, as it was just rutabaga mashed together and put in the oven, so it resembles the look of bread while tasting like… dried turnip. Although German high command was truly generous enough to give butter. But this was no ordinary butter. It was turnip paste that had the nickname of ‘Hindenburg fat’. Other introductions are fried rutabaga, rutabaga salad, rutabaga cutlet. The fact sawdust bread was considered a luxury for the front-line troops as it at least, used some flour just shows how bad the situation was. Ironically learning from these mistakes and having France produce grains for them during WW2, Germany did not have as much of a supply issue however after the war the same situation followed with the ‘Hungerwinter’ (Hunger winter).
Other notable creations at the time are ‘Ersatz coffee’ ingredients being endive spinach and chocolate. Another variant being acorn mixed with tar (yes, the things used in roads) and sugar. The first recorded soy meat in Europe also appears as ‘Friedenswurst’ (Soy Sausage) was introduced at the time. So, if vegetarians truly want everyone to embrace vegetarianism it seems all we need is another trench warfare.
Going to another Axis of evil nation, Japan during WW2 faced the same situation. Being an island nation when the American military started island hopping and closing in the quality of life for Japanese people plummeted. This was especially so in Okinawa being isolated and facing the Battle of Okinawa, the people had barely anything to eat. It was at this time ‘モービル天ぷら’ (Mobil tempura) was introduced. During WW2 one thing japan lacked severely was oil. Oil of all kinds. This is one of the reasons cited for the aggressive expansion southwards, but people still craved some fried food and so they used engine oil used in cars as it was no longer needed in a defensive position. After all, anything tastes good if fried. However, the use of engine oil of course led to severe stomach problems and even death. But the alternative being eating raw boots, it is understandable that the Japanese were just trying to find a way to eat the meager supplies that they had.
Another innovation if it can be called was during the battle of Imphal the commander of the 15th regiment 牟田口 廉也 (Mutaguchi Renya) the grand mastermind of the grand plan, proclaimed just like Genghis khan he would get the supplies off the enemies thus the lack of supplies for the operation was ignored and when inevitably several regiments reported lack of supplies during the operation he famously proclaimed ‘Japanese people are herbivores. We are surrounded by green mountains how can one claim a lack of food?’. Of course, the valiant efforts leading herbivores into the jungle ended with a disaster.
When thinking about the War and Italy one of the first stories that come to mind is the famous incident when Erwin Rommel finally cut through and relieved the surrounded Italian troops from encirclement, only to be met with the sight of Italians using precious water in the desert to cook pasta. Unfortunately, this was not the case. Italians used Canned pasta just like any other army using canned food.
Before the war, Mussolini wanted to make Italy self-sufficient using colonial imports. One example of this is “Carcade’ a drink that used tea, chicory, and hibiscus flowers coming from the African colonies at the time. However, when the war started Italy was woefully prepared for such circumstances. They lacked any form of supply-chain which could adequately sustain the war. The fact the state was forced to implement ‘orti di guerra’ (war’s orchards) where they transitioned city parks and sports fields into farmland within cities shows the lack of supply at the time. Nevertheless, Italy was faring much better than WW1 Germany as they managed to at least include brown in their diets (which was made using chaff), unlike the Germans who were solely living off of warbread.
However, one of the best pasta in the world was created near the end of the war. Renato Gualandi in 1944 to celebrate the occasion where Riccione was freed used army rations of dried food. He wanted to bring Italian and anglo-Saxon cuisine (As it was the British force that liberated the town.) together with a hint of Slovenian culinary. (inspired by a soup 'spikrofi' which was popular in Istria which at the time was part of Italy.)
He created the Carbonara.
 After all, no one would start calling it World War 1 until the second one comes if you did, you would just be tempting fate at that point.
 Hindenburg named after Paul von Hindenburg German Field marshal and president of the Weimar Republic that is well known for airship disaster, giving power to Hitler, and getting killed in the Wonder Woman film.
 Although notoriously inept he was one of the few who was under class A (Crimes against peace) but unlike almost all others prosecuted with the same class, he only received 2 years.