In July, open Soviet–German trade negotiations were under way.[88] In late July and early August, talks between the parties turned to a potential deal, but Soviet negotiators made clear that an economic deal must first be worked out.[88][89] After Germany had scheduled its invasion of Poland on August 25, and prepared for the resulting war with France, German war planners estimated that a British naval blockade would further exacerbate critical German raw material shortages for which the Soviet Union was the only potential supplier.[88]