In the time before sonar technology, submarines relied solely on the precision of sea charts, making their journeys perilous. Submarine crews lived in constant anxiety about the possibility of coming across unseen dangers like abandoned ships partially submerged in water or hidden underwater rocks that could threaten their path.

This uncertainty was a source of significant fear for those operating U-boats, as they navigated through vast and unpredictable waters. The tension of navigating blind heightened the risks involved in their missions, highlighting the challenges faced by submarines during that era.