NEW YORK (CNNMoney.com) -- Five years ago, Keefe, Bruyette & Woods insurance analyst Cliff Gallant sat at his desk on the 89th floor of the World Trade Center's South Tower, writing up a report on AIG, when he heard an explosion rock the building.

It was 8:50 a.m. on Sept. 11, 2001 and the beginning of a tragedy that decimated the Wall Street firm's corporate headquarters and left the successful forty-year old company in disarray.

KBW's new trading floor in its midtown headquarters was expanded. The company lost almost its entire trading group on Sept. 11, 2001.

"There was only a small group of people left," Gallant recalled. "There was no research department. Only myself and three other people survived from that group."

With 67 employees, including the investment bank's Chairman and co-CEO Joseph Berry, lost during the Sept. 11 attacks, many on Wall Street feared that KBW would not be able to survive.

Fast forward five years and the KBW of today is the poster-child for corporate comebacks as the company now prepares to take itself public.

The boutique investment firm, which caters to financial services companies, recently filed to go public and hopes to raise $100 million in the sale. KBW has yet to set a price for its shares or a date for its first day of trading.

It's a significant move for the company considering what it's been through during the past five years. But it's not the first time KBW has tried to go public.

In 1998, the company withdrew an offering amid weakness among banking stocks and aborted its second attempt the following year after the company's then-chief executive James McDermott revealed that he had provided his porn star mistress with insider information on bank mergers.

After 9/11, the thought of an IPO seemed far-fetched as the firm struggled to rebuild. KBW hired almost 100 new employees to its ranks in the year following the attacks and worked hard to revive its research and trading operations.

"The whole purpose of the company going forward was to dedicate it to the memories of the people that died," said one former employee. "The thought was that we have to rebuild the firm. It was therapeutic."

KBW's senior management team, including its CEO John Duffy, declined to be interviewed citing the quiet period surrounding the company's IPO filing. But in the SEC filing, the firm said the tragedy of Sept. 11 left the company with "people with the knowledge and commitment to continue, renew and significantly grow our business."

And grow it did.

Since 2001, the company has grown to 430 employees - double the amount of workers it had before Sept. 11 - and expanded its operations into Europe.

And KBW, which lost almost its entire trading staff during the terrorist attacks, now accounts for 5.4 percent of the total volume of trades of NASDAQ 100 financial stocks, according to data by Thomson AutEx.BlockDATA, a provider of trading information for the financial services industry. That's double the market share the company had at the end of 2000.

KBW now ranks as the eighth largest trader of NASDAQ 100 financial stocks, outshining larger competitors such as Goldman Sachs (Charts) and Bear Stearns (Charts).

The investment bank has also become one of the hottest mergers and acquisitions advisers to the financial services industry, garnering attention as the No. 1 ranked M&A adviser and IPO manager for finance companies last year. That helped KBW pull in total revenues of about $308 million in 2005, according to its SEC filing.

According to M&A tracking firm Dealogic, KBW served as advisor on 20 deals globally last year, valued at $39 billion, including Bank of America's (Charts) high-profile $34 billion acquisition of credit card firm MBNA.

And so far this year, the company has been an adviser on 18 mergers - valued at $21.7 billion - including Capital One's (Charts) $14.6 billion deal for North Fork Bancorp.

Despite the company's successes and its new midtown headquarters - which a company spokesman said were designed specifically on low level floors without a view out of respect for the employees - the shadow of Sept. 11 continues to haunt those that lived through that fateful day.

"I survived and, at the time, there was so much tragedy around, I was more focused on helping the families of the people that were lost," Gallant said. "It's becoming more of a normal place but I still think about it everyday."

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• Party may be over for investment banks