When the narrator introduces Colonel Cargill to the reader, his description is one of the earliest, and most extensive, uses of Heller's characteristic ironic style. The verbal irony is extensive:
His services were much sought after by firms eager to establish losses for tax purposes. [...] He had to start at the top and work his way down, and with sympathetic friends in Washington, losing money was no simple matter. It took months of hard work and careful misplanning. A person misplaced, disorganized, miscalculated, overlooked everything and opened every loophole, and just when he thought he had it made, the government gave him a lake or a forest or an oilfield and spoiled everything. Even with such handicaps, Colonel Cargill could be relied on to run the most prosperous enterprise into the ground. He was a self-made man who owed his lack of success to nobody.
The jokes come again and again. "He had to start at the top and work his way down" reverses the standard phrase in which a businessman starts at the bottom and works his way up. The final sentence is more verbal irony: he was a "self-made man" but the thing that he made was his "lack of success."
In addition to the verbal irony, there is also the situational irony of Cargill's career. Most of the time, in a capitalist economy, marketers like him are hired in order to make more money. Cargill, instead, gets hired to run businesses into the ground.
This description of Cargill, like all the ironic situations and characterizations in Catch-22, is meant to create a tone of illogic and absurdity, as part of Heller's satirical critique of the war effort. This instance also serves as an anticapitalist critique from Heller. The irony relies on the fact that it is good, under the capitalist system, to make more money, not less. By the structure of this irony, Heller casts doubt on the goodness of the American economic system, just as he attempts to undermine the logic of the American war effort.