An internal memo from has revealed that the publisher is going to great lengths to reassure their staff that there is plenty of life left in the franchise.

GiantBomb has acquired some internal communications from CEO Eric Hirschberg which essentially emphasises that Call of Duty will not suffer the same fate as which they milked to death.

Hirschberg wrote: "This is a great question and one we have thought about a lot. But there are several key differences between the two franchises worth considering. Guitar Hero quickly reached incredible heights, but then began a steady decline. Call of Duty, on the other hand, has steadily grown every single year of its seven-year existence."

He continued: "Guitar Hero was a new genre which had incredible appeal, but which had not stood the test of time. Call of Duty exists in a genre - first person shooters - that has shown remarkable staying power and wide appeal over a period of decades. Plus, Call of Duty has inspired a massive, persistent, community of players, making it perhaps the 'stickiest' game of all time."

By Ewan Aiton