On 1 September 1939, the Germans invaded Poland, and Rydz-Śmigły was named Commander-in-Chief of all Polish forces. On 7 September, along with most of the government, he evacuated Warsaw as it came under attack. Soon afterwards, Polish coordination began to suffer from issues with their communication equipment, which impaired Rydz's ability to command his forces effectively. In Brest (Brześć) on 11 September, he ordered the Polish capital to be defended at all costs. In his plan, Warsaw and the nearby Modlin Fortress were to become two redoubt-citadels in central Poland to fight on for as long as possible while the bulk of the Polish forces were to defend the Romanian bridgehead and await the counterattack promised by Poland's allies - the French and British. Unknown to Rydz-Śmigły, the Western Allies had no such plan and expected Poland to fall (see Western betrayal). This strategy was further crippled when Soviet forces invaded Poland from the east on 17 September. Realizing that mounting a defence against both Germany and the USSR was impossible, Rydz-Śmigły issued orders to his forces to begin a retreat towards Romania and to not waste men on fighting the Soviet aggressors.