Why they put actor in place of this character and send him to Germany?

In movie Where Eagles Dare (1968), In place of General Carnaby, they put an American actor Cartwright Jones. As described in the movie he is

an actor, probably second-rate but he's the dead spitting image of the General

While sending him to Germany by the British, they stage a fake air crash in German and get him caught. Why was this?

plot-explanation where-eagles-dare

Best Answer

The entire purpose of the mission is to identify a team of double agents in British Intelligence. The British have been leaking vital information to the Germans.

Admiral Rolland brings in someone he trusts - Major Smith and they plan this mission to uncover who may be working secretly for the Germans.

The entire team that is sent into Germany, with the exception of Smith and the American Lt Shaeffer are suspects of being double agents.

The team are (presumably) selected by Rolland, Turner and Smith for the 'rescue' mission. Turner and Rolland/Smith have different aims. Turner thinks the rescue is the real mission and wants to ensure that General Carnaby remains in German hands so chooses people he knows are German agents. Rolland and Smith want to choose the same people precisely because they want to confirm their suspicions about them and Turner.

Now to answer your specific question:

Cartwright Jone's part of the plan is just to give an excuse for the rescue 'cover mission' to rescue a critically important allied General. Cartwright Jones, together with Mary and Heidi are placed in Bavaria to support Smith's real mission.

Clearly they cannot use the real General for this purpose. Using Jones both gives the excuse for launching the rescue mission AND also gives Smith a way to sow confusion and doubt as to his real allegiance when he reveals Jone's true identity.

Cartwright as an American, unaffiliated to MI6 can also be trusted to not be a double-agent. Together with Shaeffer, Mary and Heidi, he's another person that can be relied upon by Smith.

Smith's plan is to observe the team, try to work out who is a double agent. He uses the meeting to turn the tables on the rest of the team and convince them to write down the names of all the German agents they are aware of, including their superior Col. Turner.

The list of names that the (now-known) agents write down is the purpose of the mission. When he reveals to Col. Turner that his name is on the list as the 'most senior German agent', Turner chooses to jump from the plane rather than go back to London and be interrogated and shot/hung as a traitor.