in which the offensive to defensive cost multiplier is calculated to be 70, versus the over 1000 number I gave. The difference is attributable to the assumptions made concerning the fraction of enemy weapons penetrating the defensive shield; in my case the kill probability was such that there was a 1% chance of a single enemy weapon penetrating the defense whereas in their calculations 10% of the enemy weapons are allowed to penetrate. Their number was historical in origin, and translates into 50 ICBMs hitting their targets in the US in a 500 missile raid, or 120 in the hypothetical near all out war. Personally I find that intolerable, recalling MacNamara's assertion that 35 ICBMs would devastate the USSR. Doubling their multiplier to 140 would in effect reduce the fraction penetrating to 1% (assuming independent ABM engagements) which in turn makes the war "survivable". Whether the number is 140 or 1000 the advantage is still overwhelmingly with the offense.
After writing this I came across the following paper by Moric & Kadyshev
https://doi.org/10.1080/10242694.2024.2396415
in which the offensive to defensive cost multiplier is calculated to be 70, versus the over 1000 number I gave. The difference is attributable to the assumptions made concerning the fraction of enemy weapons penetrating the defensive shield; in my case the kill probability was such that there was a 1% chance of a single enemy weapon penetrating the defense whereas in their calculations 10% of the enemy weapons are allowed to penetrate. Their number was historical in origin, and translates into 50 ICBMs hitting their targets in the US in a 500 missile raid, or 120 in the hypothetical near all out war. Personally I find that intolerable, recalling MacNamara's assertion that 35 ICBMs would devastate the USSR. Doubling their multiplier to 140 would in effect reduce the fraction penetrating to 1% (assuming independent ABM engagements) which in turn makes the war "survivable". Whether the number is 140 or 1000 the advantage is still overwhelmingly with the offense.