Teller's continual presence in Washington soon came to the attention of his former friend, Hans Bethe. Bethe had worked with Teller on the H-bomb but had since gone on to become a major critic of the bomb industry, and especially ABM systems. He wrote several seminal articles in the 1960s highly critical of the US Army's efforts to build an ABM system, demonstrating that any such system was relatively inexpensive to defeat and would simply prompt the Soviets to build more ICBMs.