KTTU-TV (channel 18) is a television station in Tucson, Arizona, United States, affiliated with The CW and MyNetworkTV. It is owned by Tegna Inc. alongside Fox affiliate KMSB (channel 11); Tegna maintains a shared services agreement (SSA) with Gray Media, owner of CBS affiliate KOLD-TV (channel 13), for the provision of studio space and technical services while maintaining control of programming and sales. The three stations share studios on North Business Park Drive on the northwest side of Tucson (near the Casas Adobes neighborhood); KTTU-TV's transmitter is located atop Mount Bigelow.

Channel 18 was built by the Roman Catholic Diocese of Tucson and began broadcasting at the end of 1984 as KDTU. The station, intended as a family-friendly outlet, proved to be a popular—but commercial—independent station, as well as a boondoggle for the diocese, which lost $15 million between 1984 and 1989 and unloaded it at a loss to Clear Channel Communications. The call sign was changed to KTTU-TV after the sale. Since 1991, KMSB and KTTU have been either commonly operated or owned. The station was affiliated with UPN from 1995 to 2006 and MyNetworkTV before becoming Tucson's CW affiliate in 2024.

In 1980, the Federal Communications Commission received four applications proposing new commercial television stations on channel 18 in Tucson. Tucson Telecasting, a subsidiary of McKinnon Broadcasting (one part-owner, Clinton D. McKinnon, had owned KVOA-TV from 1955 to 1962); National Group Telecommunications, whose owners were busy building KSTS in San Jose, California; and Alden Communications Group all made bids, as did the Roman Catholic Diocese of Tucson. While the three companies, all with out-of-state interests, eyed independent stations that would primarily compete with regional independent KZAZ, the diocese was motivated to file an application because its own studies found that a cable television channel would reach fewer homes. Its application proposed mostly religious programming, and the diocese boasted that it would be the first in the country to directly own a television station.

The diocese almost dropped out months later when it indicated interest in noncommercial reserved channel 27. However, it stayed with the channel 18 application and, after a settlement agreement with McKinnon, came out the winner in March 1983. The call sign KDTU was chosen, and studios were built on North 6th Avenue in Tucson. Original proposals called for a station heavy on community involvement and also catering to the majority-Hispanic diocese. Fred Allison, a market veteran from KVOA, was tapped to help program the new station; the chief engineer was a priest, the Rev. Michael Bucciarelli. As it turned out, KDTU would be more secular than it had ever planned.

Tucson's independent television market was in the middle of rapid change. Nearly immediately after KDTU went on the air on December 31, 1984, in a debut marred by transmitter problems, Tucson got its second new station in a week: KPOL (channel 40). (The two stations shared the same transmitter site in the Tucson Mountains, a 150-foot (46 m) mast painted sky blue to reduce its visual impact in an attempt to mollify property owners, and both faced unexpected setbacks getting electric service.) Despite this, the diocese projected its new station would break even within three or four years after an initial $3 million investment.

Tucson was not big enough for three independent stations—KDTU, KPOL, and KMSB, which was sold at the same time as the other two launched, rebranded, and given an infusion of cash—at a time when programming costs for this type of station were soaring nationally. Even though KDTU had more of a commercial flavor than had been intended in the pursuit of being financially sustainable, channel 18 was a drain on the diocese, frequently overbidding on syndicated shows, and its attempts to attract commercial production clients were largely ineffective, with most firms seeking out companies in Phoenix and Los Angeles. A third of the staff was cut in March 1987. Four months later, the diocese announced it would put channel 18 on the market, saying some of its programming was not a match for its mission and noting that, in trying to build the station they sought to create, the diocese was exposed to financial and philosophical pressures. (The only religious program the station aired was the Sunday Mass, which had been on KOLD-TV.) In a letter, Bishop Manuel Duran Moreno admitted to priests that the diocese had been trying to sell the station since January 1986, 18 months prior to publicly disclosing it was on the block. Trying to keep the station going was so financially taxing that the diocese neared its credit limit and had to halt building programs at its parishes. Further trouble was created when some programs the station aired, such as The Morton Downey Jr. Show, proved to not be family-friendly, generating criticism and ultimately leading to it being pulled from KDTU.

On October 21, 1988, the diocese terminated 14 employees and slashed the pay of its administrative staff by 10 percent, cutting clergy and religious support services in the process, as a result of KDTU's financial losses. While none of the station's 42 employees were affected in that set of cuts, less than two weeks later, the diocese had worse news for them: it was giving KDTU its last rites and taking it off the air on November 1. In the meantime, however, a prospective buyer emerged, and the diocese agreed to keep KDTU going while it was in negotiations. McKinnon retained a right of first refusal to match any buyer's offer from its settlement agreement years prior.

We had the best intentions. It was a good idea of bringing family entertainment to television, giving good programs that teach about the church, that teach about morality, about what's right, what's wrong. We were not in it for the money. We were in it for the service.