He is probably best known outside Norway for his role as Chief of Staff of the United Nations Truce Supervision Organization (UNTSO) between 1963 and 1970, a period which coincided with the Six-Day War between Israel and its Arab neighbours.

Taken by surprise, the Norwegians were unable to mobilize their armed forces in time to conduct an effective defence and were conquered in a 62-day campaign.

Bull noted that of the 750 Norwegians who joined the Allied air forces, 278, or more than one in three, were killed – 203 in battle and 75 in training or other accidents.

[9] He returned to Norway in 1959, but in 1963 he was offered the position as Chief of Staff of the United Nations Truce Supervision Organization (UNTSO), which he again accepted.

Bull's appointment came at a time of rising tensions, particularly between Israel and Syria, which both laid claim to territories inside the demilitarized zones.

As this was a problem with which I had been living for many years, and one which, as I had become very much aware, had at least two sides to it, I felt in conscience bound to make my own experience the basis for as calm and objective a presentation of the whole Middle East situation as I could.

For those from outside who, like myself, have become involved in this situation, the aim must always be to try to reduce the burden of suffering and injustice for all people in that area, Arabs and Israelis alike.

A calm personality, the former Commander of the Norwegian Air Force ... was able to quickly re-establish confidence and develop effective working relations with the Israeli Army and Foreign Ministry.

The Arab States could never muster the same enthusiasm for General Bull as for his predecessors, but despite Israel's appreciation of his work they were never heard to object to any of his efforts or to complain of his attitude.