Where'd the gains go? That's what investors were left asking themselves after today's market plunge. The S&P 500 (^GSPC 1.27%) nosedived by 0.9% on a day marked by red across most industries. Three stocks suffered steep downturns, however, as the National Bank of Greece (NBG.DL), Alliant Techsystems (NYSE: ATK), and Bristol-Myers Squibb (BMY 0.15%) all sank deep into the red, with shareholders of the first, in particular, taking a huge blow in the form of double-digit percentage losses.

It wasn't as if the economy gave much of a relief to investors to start the day. Even before Wall Street woke up, Europe kicked things off on a disappointing note as the eurozone's GDP gained only 0.2% growth -- an annualized 0.8% rate -- through the first quarter of the year. Economists hope for 2% annual growth down the road, so today's release is still far behind what the beleaguered continent needs to move in the right direction.

Even worse, the Dutch GDP and Italian GDP both suffered contractions in the first quarter, and only Germany's economy showed real signs of progress, with growth of 3% at an annualized rate. Germany can't do it all for the eurozone, however, and with the continent's largest economy heavily reliant on exports, the rest of Europe will need to get things going, or German growth could end up sputtering by the end of 2014.

Three stocks, one very bad day for investors

Source: Wikimedia Commons

Europe's ongoing dilemma sure isn't helping the National Bank of Greece much -- or its headache-plagued shareholders. The bank's 16% drop off today is just the latest in what's turned out to be a horrific past year for this stock, as shares have plunged by more than 79% during that time frame. The National Bank of Greece is doing its best to restructure and shore up a capital position that's been devastated by the Greek economy's collapse. Today's release from the Greek economy won't delight investors, however, as the country's GDP fell by 1.1% year over year through the first quarter of the year. It's actually a better result than Greece has been experiencing, and led some economists to double down on the European Commission's prediction that the Greek economy will grow this year for the first time since 2007. However, with unemployment still higher than 26%, and financial pillars such as the National Bank of Greece on tenuous footing, the market's still a warning sign to investors.

Add Alliant Techsystems to the list of losers today. Despite Alliant's stock doing very well through the year so far in gaining more than 23% year to date until today, shares of the ammunition and defense product maker plunged by 9.3% after what seemed, on the surface, to be good earnings. Alliant's overall revenue jumped 17% in its most recent quarter, with earnings up 32% in a top- and bottom-line beat. The company's sporting goods segment, in particular, has done very well as of late, with sales from the business, which manufacturers ammunition, gun scopes, and related items, gaining 71.5% in the quarter.

So what was the big deal? Alliant projected that its 2015 earnings would come in below analyst expectations, particularly with weakness dragging on the company's defense and aerospace division. That's a big problem considering that Alliant's defense business is the focal point of a huge shake-up in the near future: The company agreed in late April to merge the segment with launch and rocketry firm Orbital Sciences (OA), with the firms expecting the deal to close by later this year. Orbital announced in its release for the deal that it expects up to $300 million in revenue synergies and a combined backlog of $11 billion from the deal, so it's pivotal for shareholders in both stocks today that the defense and launch industries can overcome budget restraints and cuts, which have negatively affected Alliant recently.

Among the biggest stocks around, however, Bristol-Myers Squibb suffered a notably terrible day as its stock plunged by more than 6%. Bristol released a bevy of early stage clinical data on promising cancer therapy nivolumab late yesterday, but none of it impressed investors eager for more on this potential blockbuster drug -- even as the FDA awarded Bristol with a Breakthrough Therapy designation for the drug in treating certain patients with Hodgkin's lymphoma.

BMO Capital Markets downgraded the stock from outperform to market perform, part of a disappointing day for the stock, as analysts voiced concerns about the possibility of nivolumab used in combination with Bristol's Yervoy as a first-line cancer therapy. Considering the drug, in the past, has garnered peak sales expectations of $4 billion or even more, nivolumab still has plenty of potential. For analysts hoping for a megahit from Bristol's promising therapy, however, today marked a downbeat day. For investors thinking in the long term, however, don't lose hope in this drug -- or Bristol's stock -- so soon.