FRANKFURT, Feb 7 (Reuters) - Shares in tank gearbox manufacturer Renk leapt 17% to open at 17.50 euros ($18.83) each on the German company's debut on the Frankfurt bourse on Wednesday, four months after poor market conditions forced it to postpone plans to go public.

The shares were issued at 15 euros apiece, in Germany's first initial public offering (IPO) this year as equity capital markets shows signs of life after months of volatility, with several companies hoping to go public in Europe after a lull.

Renk, which supplies gearboxes for Germany's Leopard tanks, used in conflicts such as the Ukraine war, on Tuesday increased its IPO by 50 million euros to sell around 500 million euros shares in its private placement.

Shares worth 100 million euros went to the German-French tank manufacturer KNDS (KMW+Nexter Defense Systems), one of Renk's largest customers. KNDS now holds 6.7% and has the right to later increase it to a blocking minority of 25%.

Last October, Renk and its owner, private equity group Triton Partners, pulled a planned IPO at the last minute, citing a "clouded" market environment.

They resumed the issue on Monday but limited it to professional investors to shorten the process.

Advisers on the IPO included investment banks Citigroup , Deutsche Bank, Goldman Sachs and JPMorgan.

Private equity group Triton bought Renk from the Volkswagen Group in 2020 for almost 700 million euros.

Optimism around IPOs has grown in recent weeks, with central banks signaling interest rates may have peaked and volatility down to levels that dealmakers see as conducive to transactions.

Defense stocks, including Germany's Hensoldt, have been on the rise after dipping in the autumn, providing a better backdrop for Renk's listing. ($1 = 0.9292 euros) (Reporting by Emma-Victoria Farr, Editing by Rachel More, Miranda Murray and Emelia Sithole-Matarise)