This morning's bombings in London were horrific, but they shouldn't distract investors from a few core strategies, Jim Cramer said on his "RealMoney" radio show Thursday

Cramer discussed the best trading responses to this morning's subway bombings in London's public transport system. Early in the show, he put aside the notion that the U.S. market's afternoon rally makes American's "unfeeling" or "uncaring."

"Exogenous events will always play roles in the market," said Cramer. "But after 9/11, the notion of terrorism as an event that can wreck our markets has forever changed."

Traders recognize terrorism is part of life, Cramer said. They need to be able to decide quickly what sectors it will affect. "And if it does not look like a sector will be affected, then we step in and buy."

Today was a good chance for U.S. buyers as European traders beat down shares ahead of the U.S. open. Cramer partly attributed the European response to profit-taking, saying "our markets have not been as robust as the Europeans so they have more profits to take."

Any additional fallout will be positive, in Cramer's opinion, as the British have traditionally been tough on terrorism.

Cramer said he used this morning's weakness to buy the tech and defensive stocks that the Europeans were dumping. In other words, he nibbled at semis and aerospace names.

On the other hand, he moved out of bank stocks when they rallied later in the day.

"I'm astounded that the Fed did not blink at all when I was on vacation," said Cramer, who has been away for about a week. A lot of bank stocks have been buoyed by their high yields recently, but another two rate hikes means that cash will be more attractive. So he advised swapping out of the banks.

Stump Cramer Day

Cramer returned to the radio waves just in time for one of his favorite segments: "Stump Cramer." In this segment, Cramer's callers test his stock knowledge for tickers he may not be aware of. If he blanks on their ticker, then the caller wins a copy of his book.

The first caller couldn't pull it off, with his choice of UQM Technologies ( UQM). Cramer recognized the company as a maker of electric motors for hybrid cars. Cramer said it was totally speculative and losing money; in other words, not the type of company he likes to buy. He offered Quantum Fuel Systems Technologies Worldwide ( QTWW) as a better play.

Another caller offered biotech player EntreMed ( ENMD). Cramer recognized the company, and reiterated his dislike for its shares.

A few callers did win books to supplement their summer reading, however, by stumping Cramer with recent IPOs.

Among the companies that Cramer missed, but promised not to miss again, were paper manufacturer Xerium Technologies ( XRM) and Massachusetts-based Ben Franklin Bancorp ( BFBC).

Cramer also promised to do some homework on Houston oil services company ENGlobal ( ENG), a $4 stock that Cramer seemed to like at first glance.

Oil services stocks have been a favorite of Cramer's for a long time, although he admitted Thursday that he sold some of his shares of Halliburton ( HAL) so as not to be piggish.

Cramer also defended himself from a Boston Herald reporter that took him to task for pounding the table on UnitedHealth ( UNH). Cramer says he has been positive on UNH for the past five years so he is unapologetic for recommending it, especially in the wake of its purchase of PacifiCare ( PHS), which he views as positive.

Summing up, Cramer said that reacting to the news of this morning's tragic bombing in Europe does not make U.S. traders mercenaries. It's just a new angle to the business in the wake of 9/11.

"Nobody has ever made a dime panicking, but we have made a lot of money keeping cool when others panic," said Cramer.

At the time of publication, Cramer was long Halliburton and UnitedHealth.

James J. Cramer is a director and co-founder of TheStreet.com. He contributes daily market commentary for TheStreet.com's sites and serves as an adviser to the company's CEO. Outside contributing columnists for TheStreet.com and RealMoney.com, including Cramer, may, from time to time, write about stocks in which they have a position. In such cases, appropriate disclosure is made. To see his personal portfolio and find out what trades Cramer will make before he makes them, sign up for Action Alerts PLUS. While he cannot provide personalized investment advice or recommendations, he invites you to send comments on his column by clicking here. Listen to Cramer's RealMoney Radio show on your computer; just click here. Watch Cramer on "Mad Money" at 6 p.m. ET weeknights on CNBC. Click here to order Cramer's latest book, "Real Money: Sane Investing in an Insane World," click here to get his second book, "You Got Screwed!" and click here to order Cramer's autobiography, "Confessions of a Street Addict."

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