Schiffer's
German Armored Rarities 1935-1945 has brief descriptions of both of these vehicles. 30 VK 1801 were built, all were delivered in 1940. In May of 1942, 5 VK 1801 were issued to 1st Company of Pz.Abt.z.b.V.66 to be used originaly during invasion of Crete (Operation Herkules), but instead were sent to near Leningrad in Russia. In Russia, 1st Company of Pz.Abt.z.b.V.66 was attached to 29th Panzer Regiment of 12th Panzer Division, where they remained in small number till July of 1943. In May of 1943, 5 VK 1801 were issued to 2nd Polizei Panzer Company (neu) from Vienna, which was transfered to the Eastern Front. All tanks were lost by August of 1944. In March of 1943, 8 VK 1801 were issued to 1st Panzer Regiment of 1st Panzer Division and saw service in Russia, Yugoslavia and Greece to the end of the year. As for the VK 1601, 22 were built of the initial series ordered, but production was halted. 7 of them saw service with the 12th Panzer Division in Russia in 1943. In 1944, a VK1601 was found minus it's turret, and with a jib crane fitted to create a rudimentary BergePanzer. I have 4 photos of a VK1601 and six photos of a VK 1801.