McLachlan won't say how much the bank is spending on the campaign but said it had never done anything on that scale in the past.
McLachlan said he believed the campaign would kick off a major growth period for the bank.
He wants to double its current 128,000 customer base in the next five years and then keep doubling it every five years. "I think it is very realistic to do that."
He pointed to Kiwibank, which grew by 800,000 customers in its 10 years.
"It's not likely we will grow that fast. But this business should be doubling every five years."
McLachlan said co-operative banking was a new concept to New Zealand but it was not new in other parts of the world.
McLachlan said it was popular in Europe and North America where the key was giving profits back to customers.
On June 28, the Co-operative Bank gave $1 million back to its customers in its first ever rebate.
McLachlan said the bank hoped to be in a position to pay some money out every year.
It is also boosting its branch network, particularly in Auckland.
"We have got representatives from Whangarei to Invercargill but we have only got one branch on Auckland's North Shore."
He wants to add 10 new branches to its current seven in Auckland over the next few years. Two are planned to be open in September. "Auckland is where we are majorly underdone."
The bank will also re-open a branch in Christchurch replacing one that was forced to close because of the earthquakes.
It currently has 31 branches throughout the country but hopes to grow that to 45 in total.
"Auckland is 40 per cent of New Zealand - if we haven't got 40 per cent in Auckland our starting point is we are a little underdone."
While fewer people go into their bank branch these days, McLachlan said many still liked to know they could go into a branch even if they don't use them.
"I am an absolute advocate that branches remain the heart and soul of the bank."
The bank is also moving some of its existing branches to meet customer demand and growth.
New branches in Auckland will operate seven days a week.
McLachlan is based in Wellington four days a week, but commutes back to Auckland for the weekend.
"So much business growth is in Auckland - we can't be successful as a national business unless we really know and understand Auckland."
The bank will hold its annual general meeting in Auckland at the end of the month.