1. 这不是 as 引导的“让步从句”。

2. as he did 是方式状语，修饰现在分词 commanding。说明实际上已做到。

3. 为了理解起见，省掉 as he did 和 however 后，Commanding only seven divisions in his Tenth Army， 这是现在分词短语，放在句首表示“原因”。commanding 的宾语是 only seven divisions in his Tenth Army，至此，句子结构就很清晰了。

Commanding （as he did, however,）only seven divisions in his Tenth Army, （原因状语）of which the 16th Panzer alone was at full strength, （是seven divisions 的定语从句）he was obliged to commit what strength he had against the northern edge of the bridgehead with the aim of denying the invaders a swift exit towards Naples.（句子主干）

4. 在 as he did 中，did 是个替代词，替代前文的动词。既然是方式从句，它既可以修饰谓语动词，也可以修饰非谓语动词。例如：
He cared deeply about his men as he did about so many. （修饰谓语动词cared）
正像他对许多人做的那样，他深深地关心着他的战士们。
I also hoped that, speaking Russian fluently as he did, he might become an important link with the Soviet High Command. （修饰非谓语动词 speaking）
他既然会说流利的俄语，我也希望他成为同苏联最高司令部进行联系的重要桥梁。