Leaked documents show how McDonald's plans to win the 2021 chicken-sandwich wars. Here's everything we know about the looming fast-food battle.

• McDonald's improved chicken sandwiches will roll out nationally in late February, a leaked menu viewed by Business Insider shows.
• The memo confirms the sandwich aims to take a page out of Chick-fil-A's playbook, with the same ingredients and similar spicy and deluxe variations. It's to be served in a foil bag.
• Chains including KFC, Wendy's, and Burger King have either been testing or rolling out new chicken sandwiches in recent months.

McDonald's is taking a clear aim at Chick-fil-A in the 2021 chicken-sandwich wars, an internal memo viewed by Business Insider shows.

The fast-food giant appears set to launch three chicken sandwiches, made with a new "thicker and juicier" chicken fillet, on February 24, McDonald's confirmed.

Advertising for the improved chicken sandwiches is set to roll out in early March.

The new Crispy Chicken Sandwich will feature chicken and crinkle-cut pickles served on a buttered potato bun.

If the sandwich sounds familiar, it might be because you've eaten Chick-fil-A's chicken sandwich, which also features the simple combination of a chicken fillet, pickles, and a buttered bun. For comparison, Popeyes tops sandwiches with mayo, as do most fast-food chicken sandwiches.

McDonald's is also set to debut the Spicy Crispy Chicken sandwich, made with crinkle-cut pickles and a new spicy pepper sauce, and the Deluxe Crispy Chicken sandwich, with tomatoes, shredded lettuce, and mayonnaise.

(Chick-fil-A also serves a spicy sandwich, made with seasoned chicken, and a deluxe sandwich, with tomatoes, lettuce, pickles, and American cheese.)

Except for the deluxe option, the new crispy chicken sandwiches will be served in a foil bag - a presentation style that Popeyes and Chick-fil-A use, but that McDonald's has previously eschewed.

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Here's everything we know about the competitors in the 2021 chicken-sandwich war

In November, McDonald's announced plans to introduce the Crispy Chicken Sandwich in the US in early 2021.

"Developing a reputation for great chicken represents one of our highest aspirations," McDonald's head of its US business Joe Erlinger said at the time. "We want customers to choose McDonald's for chicken because of the unique, craveable flavor that they can only get under the arches."

McDonald's isn't the only chain gearing up for a battle of the chicken sandwiches in 2021. Here's the lineup of chains that are testing sandwiches or have already rolled out an updated chicken sandwich:

• Burger King was spotted testing a new chicken sandwich in October. UBS analyst Dennis Geiger said in a note in December that a 2021 chicken sandwich launch is sparking "notable optimism" among franchisees. (Burger King declined to give further details on a launch, saying in a statement: "The King must eat like a king. So, we're constantly testing new items to satisfy his cravings.)
• KFC launched a chicken sandwich test in May. "We wanted a chicken sandwich that really lives up to our legacy as the fried chicken experts and, let's face it, ours wasn't the one to beat," KFC US Chief Marketing Officer Andrea Zahumensky said at the time in a press release.
• Wendy's released a new chicken sandwich in October. The new "classic chicken sandwich," replaced the "homestyle chicken sandwich" on Wendy's menu.
• Church's Chicken added its first chicken sandwich to the menu in late October.
• Jack in the Box debuted the Cluck Sandwich in December. The new sandwich is thicker than the chain's existing chicken sandwich.
• Zaxby's is serving a new chicken sandwich in test locations and announced in December that the sandwich will roll out nationally in 2021. The chain tweeted in October: "The chicken sandwich war ain't over yet."
• Whataburger rolled out a new spicy chicken sandwich in September.

New sandwiches will have to compete with Chick-fil-A and Popeyes

Two chains that haven't made major chicken-related announcements are Chick-fil-A and Popeyes.

Chick-fil-A calls itself the home of the original chicken sandwich. Unsurprisingly, the chain hasn't made any major updates to its classic sandwich in decades. As a private company, it is difficult to know how Chick-fil-A has fared financially in 2020 - but, as one of the industry leaders in drive-thru technology, it is likely thriving in the pandemic.

Popeyes, meanwhile, is still basking in the success of its 2019 chicken-sandwich launch. In late October, parent company Restaurant Brands International reported that Popeyes sales were up 21.5% in the most recent quarter. Restaurant Brands International CEO José Cil said on a call with investors that the chicken sandwich continued to be "the largest single driver of sales growth."

"This result comes on top of 10% comparable sales growth during the third quarter of 2019, which is when we initially launched the chicken sandwich in August," Cil said. "Millions of people have been coming back for the chicken sandwich, but it's been really exciting to still see a significant number of first-time purchasers in Q3."

What does it all mean?

Industry insiders have been keeping a close eye on the sandwich wars.

Steve Crichlow, the founder of Compass Restaurant Consulting, wrote in a November report that increased competition will affect Popeyes' "domination of the chicken sandwich market."

"From what we have tested and heard (excluding McDonald's version), we expect Wendy's to have the biggest impact," Crichlow wrote. "Not because it is better but rather because Wendy's customers are very loyal to the brand and those that might be currently going to Popeyes to get their Chicken Sandwich fix will come back to Wendy's."

Chicken-breast prices are at five-year highs, according to FreightWaves' newsletter The Stockout, reaching $3.41 per pound. Fast-food chains' success during the pandemic have helped meatpackers regain lost restaurant sales, Bloomberg reports.

"We are encouraged by reports of a chicken-sandwich war in 2021," Sanderson Farms CEO Joe Sanderson said on a call with investors in mid-December.

Sanderson - the chief executive of one of the largest poultry producers in the US - added: "We wish all the participants much success."