Schubert was born in Chemnitz and studied mathematics and physics at the Universities of Frankfurt am Main, Zürich and Heidelberg, where in 1948 he received his PhD under Herbert Seifert with thesis Die eindeutige Zerlegbarkeit eines Knotens in Primknoten.
[2][3] From 1948 to 1956 Schubert was an assistant in Heidelberg, where he received in 1952 his habilitation qualification.
decomposes as a connect-sum of prime knots in a unique way, up to reordering.
[4] After this proof he found a new proof based on his study of incompressible tori in knot complements; he published this work Knoten und Vollringe in Acta Mathematica, where he defined satellite and companion knots.
During World War II Schubert worked as a mathematician and cryptoanalyst in the Wehrmacht signals intelligence organisation, General der Nachrichtenaufklärung as an expert on Russian and Polish Army Ciphers and Codes as well as Agents codes and ciphers,[6] obtaining the rank of lieutenant (German: Leutnant).