Hungary–Romania relations
During World War II, Hungary and Romania became allies and participated in the war against the Soviet Union. But after the coup on 23 August 1944 Romania switched sides and fought against Hungary. Consequently, Soviet and Romanian troops invaded Hungary, occupied Northern Transylvania by October 1944 and re-established the Romanian administration in the region in March 1945. The 1947 Treaty of Paris reaffirmed the borders between Romania and Hungary as originally defined in Treaty of Trianon 27 years earlier, thus confirming the return of Northern Transylvania to Romania.
Naval history of World War II
The Romanian Navy was the largest Axis naval force during the naval war in the Black Sea. When the country joined the war in mid-1941, its main force comprised 5 destroyers (two "Regele Ferdinand"-class and two "Mărăști"-class plus the sea-going torpedo boat "Sborul"), 1 submarine ("Delfinul"), 1 minelaying frigate ("Amiral Murgescu"), five sea-going monitors (four "Mihail Kogălniceanu"-class and one "Sava"-class), three coastguard cruisers (all "Bistrița"-class), six escort corvettes (four of the French-built "Sublocotenent Ghiculescu"-class plus the converted torpedo boats "Năluca" and "Smeul"). Two more submarines, "Marsuinul" and "Rechinul", were launched a short while prior to Romania's entry into the war, but they were commissioned only in May 1943. Also acquired in 1943 were five Italian CB-class midget submarines. By May 1944, two Romanian motor torpedo boats ("Viscolul" and "Vedenia") were fitted for escort service.