Troops who receive a FedEx delivery at Prince Sultan Air Base in the Saudi Arabian desert won't be the first to open the package. Every item delivered to the main gate must be unsealed and inspected by security guards before it can enter the compound.

Such invasive procedures are a way of life at that sand-blown USAF outpost, home to 3,600 airmen. Cargo trucks and unregistered cars seeking entry can sit for close to an hour while guards slide underneath the vehicle, pry into body cavities, and even peer into the tailpipe looking for explosives. Precautions like these may bottle up commerce and make coming and going a chore, but they keep devastating terrorist bombs outside the base perimeter.

The Air Force learned to use such techniques in the hardest way imaginable. In 1996, terrorists detonated a truck bomb beside Khobar Towers, an apartment block in Dhahran, Saudi Arabia, used as a barracks. The blast killed 19 and injured 500. Overruling the Air Force, Secretary of Defense William S. Cohen held the wing commander responsible and stripped him of promotion, effectively ending his career.

The Air Force intensified new security procedures worldwide. Force protection, which the Pentagon claimed was underemphasized and underfunded at the time of the attack, has become such an overriding concern that airmen in Saudi Arabia generally aren't allowed off base unless their jobs require it.

And Now, the Navy's Turn

The Navy has been going through the same drill ever since Oct. 12--the day terrorists bombed the destroyer USS Cole in Yemen's Aden harbor, killing 17 and injuring 42. The attack, sprung on the ship's crew during a refueling stop, pushed the sea service into a massive review of force protection procedures.

Like the Air Force, the Navy seems to be undergoing a fundamental shift in its approach to protecting its people. "The attack revealed weaknesses in our force protection program," acknowledged Adm. Vernon E. Clark, Chief of Naval Operations, in his endorsement of the Navy's review of the Cole incident. He specifically cited "inconsistent force protection schemes" and "inadequate guidance on interpreting and executing existing force protection measures."

After the 1996 Khobar Towers bombing, the Air Force did an immediate review of security and quickly changed numerous procedures. The Navy, however, was more relaxed about the threat. In the fleet, this was hardly a secret, as attested by the skipper of one ship that had refueled in Yemen shortly after the 1996 Khobar Towers attack. He recalled, "Force protection was not Job 1." He and his sailors clearly understood, he explained, that the Navy had made a conscious decision to take risks in order to show the flag in the Middle East region.

That's changed. Since the Cole bombing, the Navy has taken steps resembling those instituted by the Air Force after Khobar Towers. The 1996 attack, for instance, led the Air Force to build fences, berms, and other physical barriers to keep any intruders hundreds of yards away from work or living areas. When Saudi officials wouldn't allow such construction around Khobar Towers itself, the Air Force pulled up stakes and moved everybody and everything to the remote confines of P-SAB, where human lookouts and sensors can spot and monitor approaching vehicles at a distance of more than a mile.

The Navy, seeing the protective value in these measures, recently enacted waterside versions. In Groton, Conn., Norfolk, Va., and several other East Coast ports, the Navy is using oil booms and other floating barriers to establish "exclusion zones" around its ships. Civilian vessels are not permitted inside. At other harbors, the Navy has erected signs warning unauthorized craft to stay out and has set up sensors to detect violators.

The Navy operates a test bed of security enhancements in the harbor in Bahrain, the Gulf nation in which the US maintains its Navy Fifth Fleet headquarters. That system is one of the most sophisticated in the world: Radars on land and at sea track ship traffic more than five miles out. Underwater sonar buoys and other sensors form a "swimmer detection system" that can detect the movement of a lone scuba diver. Video cameras on the masts of US ships zoom in on traffic of special interest. An unmanned boat rigged with a small camera patrols the harbor, sidling up to suspicious vessels for a closer look.

The Navy might end up piggybacking on many other Air Force security developments. In 1997, for instance, the Air Force stood up a force protection battlelab at Lackland AFB, Tex., to develop new security technologies and evaluate new anti-terrorist tactics and strategies. It developed vehicle search strategies-that is, good ways to detect bombs in cars. Lab workers rigged cars with explosives so tests could proceed under realistic conditions. "We have to learn to do it by doing it for real," declared Air Force Brig. Gen. James M. Shamess, the director of USAF security forces. Proven techniques are quickly shipped out to places like P-SAB, where security forces probe every opening of vehicles permitted onto the base.

"First-In" Unit

The post-Khobar Towers Air Force established a unit that specializes in force protection and that can augment or supplant the security provided by a unit's own security forces. The 820th Security Forces Group, based at Moody AFB, Ga., is a "first-in" unit that quickly establishes security at forward operating bases during a contingency.

The unit already has faced a major test. During the 1999 NATO air campaign over Kosovo, the Air Force dispatched the 820th to Tirana, Albania, to help safeguard airmen and troops taking part in relief operations. The 820th took over for a much smaller unit sent by US Air Forces in Europe. The USAFE unit thereby was freed to tend to other needs in the busy theater.

The 820th, when completely filled out in September, will have about 620 troops. It will be able to design or revise force protection plans for units at bases throughout the world.

Now, the Navy is signaling its own need for specialized units. In November, Fifth Fleet requested 100 additional coastal-warfare specialists--Navy and Coast Guard port security experts--to help maintain force protection in Bahrain. More centralized force protection planning, such as that provided by the Air Force's 820th, may be a particularly useful model for the Navy. Up until the Cole attack, every ship's force protection plan would be designed by the skipper.

The Joint Staff publishes guidelines for force protection. However, many of the measures are advisory only. For example, the guidelines for a ship under Threatcon Bravo--the mid-level state of alert under which Cole had been operating in Aden--state that a ship's commander should deploy picket boats to interdict approaching craft "if the situation warrants." Cole's skipper, Cmdr. Kirk S. Lippold, didn't do that. Investigators found that if he had, it could have helped prevent or mitigate the attack.

On Jan. 19, the institutional Navy delivered its official conclusion: The skipper didn't need to go down with the ship, at least not this time. Navy head Clark concluded that, while Lippold made some mistakes, he should not be punished for the incident.

Clark reached that conclusion even though Navy investigators found Lippold took only half of the 62 protective measures he should have taken when Cole pulled into Aden harbor. Working-level Navy investigators recommended disciplinary action for Lippold and three other officers.

However, senior commanders disagreed. In a forceful rebuke to the investigators, Adm. Robert J. Natter, commander in chief of the Navy's Atlantic Fleet, argued that even if Cole had been on a higher alert status, it could not have thwarted the attackers. That's because the bombers never showed any "hostile intent" that would have justified waving off or firing upon local citizens. Clark backed up Natter.

"There is a collective responsibility," said Clark. "We all in the chain of command share responsibility for what happened."

Cohen agreed with the Navy. This time, no one would be held individually responsible.

Cohen the First

Five years ago, when the issue was the attack on Khobar Towers, the story was very different.

Initial probes pointed to intelligence problems as the principal cause of the disaster. Secretary of Defense William J. Perry blamed the "inconclusive nature of the intelligence," while Rep. Floyd D. Spence (R-S.C.), House National Security Committee chairman, said there were "intelligence failures" at Khobar Towers.

Then came a report by retired Army Gen. Wayne Downing. In a surprising turn, he put blame squarely on Brig. Gen. Terryl J. Schwalier, commander of the 4404th Wing (Provisional), members of which were housed at the Khobar Towers complex. Downing said Schwalier "did not adequately protect his forces."

Subsequently, the Air Force conducted two comprehensive inquiries. Both found that Schwalier had done all that could have been reasonably expected of him. The wing commander had taken 130 specific actions to improve security in the year before the bombing and implemented 36 of the 39 recommendations from the most recent vulnerability assessment.

However, that didn't satisfy Cohen, who was new to the job. He conducted his own review, after which he declared that Schwalier "could have and should have done more" to defend Khobar Towers. He canceled Schwalier's previously approved promotion to major general.

In the endgame of the Cole investigation, however, Cohen demonstrated a reversal of form. "Navy leaders have concluded that the overall performance of the captain and his crew does not warrant punitive action, and I agree with that conclusion," he said. Cohen left office the next day.

In the cases of both Khobar Towers and Cole, intelligence deficiencies figured heavily. Air Force officials say they have succeeded in formulating ways to get intelligence about a terrorist threat to the people who need it. An improved push-pull system designed after the 1996 bombing places emphasis on getting national-level intelligence-information gathered by spies, satellites, or other top secret efforts-down to unit commanders in the field.

Unit-level threat working groups evaluate fragmentary intelligence tidbits to see whether they can divine a threat to their region or installation. When commanders need to "pull" additional information out of the system, they can call Air Intelligence Agency at Kelly AFB, Tex., around the clock for quick updates or assistance with analysis. Any newly determined threats are quickly sent back up the chain of command, and ideas for improving force protection are circulated among commanders and force protection officers.

As its review of force protection procedures continues, the Navy may develop new ideas to share with the Air Force and other services. Take, for example, a recent seminar wargame sponsored by the Navy and Marine Corps and run by the Potomac Institute for Policy Studies, a northern Virginia think tank. Out of the wargame came several recommendations for improved force protection techniques, from the simple-mounting more guns on ships-to the complex. In the latter category would be:

Installation of devices that can detect explosives from a distance.

Use of "vehicle stoppers" that can electronically shut down the engines of certain cars.

Robots that can detect bombs and, if necessary, disable threatening vehicles with small-arms fire.

Retired Marine Corps Col. Gary Anderson, the leader of the Potomac Institute wargame, said the military services need to look beyond their own security strategies: "We need to think about an interagency approach to force protection."

One of the most important lessons for the military services may be learning from each other. The Cole bombing, for instance, prompted the Air Force to go back and take another look at post-Khobar security procedures. USAF investigators discovered no glaring deficiencies, but security officials are hardly relaxing.

"You can never say ... in force protection that you're finished," said Shamess, the security forces director. "Force protection is one of the most difficult things in the world. Terrorism is worldwide. It goes on forever."