One of the first occasions that navigators became aware of the potential problem generated by the (then) recently-invented radar, was the so-called radar-assisted collision which occurred outside of New York between the Stockholm and the Andrea Doria in 1956. Forty-seven lives were lost in the Andrea Doria and five on the Stockholm.

Radar (Radio Detection And Range) had been invented and began its sea service during the Second World War. Its use had been, as its name implied, to give initial warning of, and the range of, another vessel on a simple Cathode Ray Tube. As the system was enhanced and the Plan Position Indicator (PPI) style of display came into prominence, complete stretches of the coastline were shown. Its usage was enhanced so that ships began to be navigated by radar. However, the navigator himself was still very much in touch with the natural elements, through the very open design of the bridge at that time.

Following the Stockholm/Andrea Doria tragedy, navigators came to terms with the fact that their PPI view of the world was a relative one rather than the actual world. Plotting the observations became the norm.