Sentence:  If it is essential in our interests to maintain a quasi-permanent position of power on the Asian mainland as against the Chinese then we must be prepared to continue to pay the present cost in Vietnam indefinitely and to meet any escalation on the other side with at least a <WSD>commensurate</WSD> escalation of commitment of our own. 
Meaning of the word marked with <WSD> tags:  Of a proportionate or similar measurable standard.