"At The Sharp End" is a supplement for the core rules that covers the setting up of a Chain of Command campaign.
The supplement comes as a PDF, of 48 or so pages, for only £6, and divides into four sections.
The first covers the basic concept of the ladder campaign: essentially, the system treats a campaign as moving up or down a ladder of scenarios depending on the winner of the previous scenario. At its most basic, you can do this without a campaign map, just using the suggested scenarios from the core rule book in the appropriate order. Next up, one can design the scenario with a basic sketch map - just a simple almost-doodle that suggests the terrain etc for each of the locations on the ladder - Rich's Western Desert campaign on the TFL blog is an example of this. The final approach is to use a real map, potentially of a real campaign, and pick out suitable table-sized areas for each rung of the ladder.
Section two covers the mechanics of setting up each rung on the ladder, and what happens before and after. Section three delves deeper into the Big Men in your platoon, and how they affect the campaign and vice versa. The platoon CO's performance is tracked on three scales - his own performance, how the battalion CO sees him and how his men see him, There are also tables for generating background for your Big men.
Section four is an example of a detailed map campaign, using readily available source material, based on events round Hill 112 during the NW Europe Campaign, and does a very good job of demonstrating how a fairly moderate outlay in time and expense can create a surprisingly detailed campaign. For all the examples in the book are largely NW Europe, the actual system is completely generic to WW2 (and the Spanish Civil War without loss of generality).
At its most basic, as I said? This supplement is pretty much a turn-key campaign set up guide, if you're happy playing a linked set of scenarios with the same 'characters', it's no more effort than doing the same for Dux Britanniarum. The more you put in, the more you can get out, though. I really like it: it's got me thinking of several campaign ideas already.
In short? If you want to do anything more than just one off scenarios with Chain of Command (and who wouldn't?)? Go out and buy - it's worth every penny.
[Disclaimer: I did proof-read an advance copy this week. But I'd buy it anyway!]