Gavin Williamson said the units, which include Bloxwich Academy, Q3 Academy in Langley and Colton Hills Community School in Wolverhampton, would offer 'unrivalled opportunities' to develop new skills.
A total of 26 new units have been announced, forming part of the Government's target to have a total of 500 running by 2020. A total of 453 have now been approved.
WATCH: Gavin Williamson meets cadets in West Bromwich
Mr Williamson made the announcement during a visit to the Phoenix Collegiate School in West Bromwich, which has been running its own cadet unit for the past year.
He also said he wanted to see increased recruitment for Britain's armed forces in the wake of 'ever growing threats', saying there was 'a real positive sense' that Britain was 'trying to get its armed forces in the right place'.
“Being a cadet offers students unrivalled opportunities to develop new skills, enjoy unforgettable life experiences, and be inspired by our world class armed forces," Mr Williamson said.
“I’m delighted to announce a new round of cadet units in schools across the UK, showing our commitment to ensure students from all backgrounds have the chance to fulfil their potential."
During his visit the Defence Secretary chatted with staff and cadets, some of whom he presented with qualification certificates.
Two of them attempted to teach him how to do a fisherman's bend knot, a technique which Mr Williamson appeared to find beyond his capabilities.
Mr Williamson has made recruitment one of his key issues since taking over as Defence Secretary in November.
Responding to a recent report that said the British Army faced its biggest shortfall in recruitment for a decade, he said: "We want to be getting out in the community more and making sure the Royal Navy, the Royal Air Force and the Army are all growing.
"We need to get the message across that joining the armed forces allows people a high level of training with amazing opportunities.
"We want to make sure we recruit as many people as we can."
He said the latest British Army recruitment campaign, launched in January, had been a 'major success', with a 'large increase in the number of people applying to join up this year.
"In the last month Army numbers grew by 500 and that's what we want to continue to build on," he said.
"We want to make sure that we are reaching out into communities all over the country, encouraging them to join up."
On the ongoing defence spending review, Mr Williamson said: "Defence spending is growing over the next few years, an extra billion pounds this year, with £800 million [for the Dreadnought programme] on top of that, so there is a real positive sense that we are trying to get our armed forces in the right place to deal with the ever increasing threats that this country faces."
Mr Williamson has also announced the launch of the first ever Veterans Strategy, which is recruiting leading military charities to help with the push to support ex-service personnel.
"It is going to make a real difference," he said.
"People who join the armed forces are willing to risk everything to defend this country. I think our nation owes them a great debt, not just when they serve, but also when they leave.
"Our duty and responsibility to them is something that lasts a lifetime."