As America's military shrinks thanks to defense reductions and the nightmare known as sequestration, defense planners face an ever increasing challenge by nations who wish to limit military access to areas of the globe vital to their strategic interests. The question of access could end up being the strategic challenge of the 21st century, but will America's armed forces be up to the challenge?

The strategy, dubbed Anti-Access/Area-Denial, or A2/AD -- while nothing new but a fancy term for layered defense across multiple domains such as land, sea, air, cyber and space seeks to wedge an asymmetrical dagger in the heart of America's seemingly insurmountable military edge. Weapons such as ultra-quiet diesel submarines, advanced mines, anti-ship weapons, and even cyber or anti-satellite weapons would seek to engage U.S. forces an in an effort to slow, stop or deter enemy combatants from entering a combat zone or contested geographic areas.

The nation that is most associated with A2/AD -- and rightly so -- is the People's Republic of China (PRC). The PRC has developed a robust anti-access capability that certainly would pose a challenge to any force that wished to operate in the near seas along its coasts and near what is commonly referred to as the first island chain. China's military has intently studied America's victory in the First Gulf War and subsequent operations but also recalls a bitter experience where it had no response to U.S. power -- in the 1995 - 1996 Taiwan crisis. In areas of strategic tension such as the East and South China Seas to the now calm but still contested area around the Taiwan Strait, China could shower any target with an abundance of cruise and ballistic missiles from various platforms. Combined with robust cyber, submarine, and surface forces that could be synergized to deny access across multiple domains, U.S. and allied forces could find themselves constrained unless they are willing to accept high levels of casualties not seen in recent memory.

But one does not need to have the robust resources of the world's second largest economy to develop a potent A2/AD strategy. Iran is also developing its own anti-access approach. With a small but capable force of Russian build diesel submarines, mines, various types of missiles and a growing cyber capability, Iran has certainly embraced A2/AD. While certainly not as capable as the PRC, U.S. forces that operate close to Iran's coast as well as maritime shipping that must transit the Strait of Hormuz are certainly in the capable crosshairs of Iran's forces. And with Iranian threats to close the straits in time of a crisis, such threats should be taken seriously. If American forces do attempt at some point to halt the progress of Tehran's nuclear program with military force, anti-access systems will be Iran's weapon of choice.

America's access problem however does not stop with Iran in the Middle East. Syria's A2/AD centric purchases have figured prominently in the news just recently. Damascus will reportedly acquire from Moscow the S-300 air-defense system. Such a system could constrain the ability of anyone considering intervening in Syria's bloody civil war, or future Israeli actions to prevent weapons transfers to Hezbollah. Russia has also reportedly sold to Syria advanced supersonic anti-ship cruise missiles. Called the Yakhont, it speeds to its target at Mach 2.5 and has a reported range of 300 kilometers. Such weapons, with properly trained crews, would certainly constrain military options for intervention and could embolden President Assad to press forward at a time when the world seeks his departure.

While depictions of access challenges in various geostrategic hotspots sound quite grim, America's military is more than up to the challenge. Even as U.S. military planners will face access challenges with diminishing resources, America's armed forces remaining the world's best by whatever measure employed. The best solution to solving the access challenge is a clear shift in priorities to meet the threat environments of the future. This has clearly begun with the creation of the AirSea Battle operational concept and the Joint Operational Access Concept. However, words and defense papers must now transform into action. For example, America's carriers will clearly need to operate further away from coastlines stacked with robust A2/AD missiles. Systems such as the recently tested X47-B and the follow-on Unmanned Carrier Launched Airborne Surveillance and Strike System (UCLASS) are important in ensuring carriers do not becoming obsolete. U.S. planners must also continue to fund and consider increasing the amount and types of nuclear submarines that will need to operate in areas of contested access. Submarines that can carry large amounts of missiles with long-ranges that can degrade the command and control systems of anti-access nations will be of vital importance. Cyber forces must also be ready to attack the ability of advanced missile systems to target vessels on the open ocean.

While the above is certainly not a comprehensive list of ways to negate anti-access challenges, it would certainly be a good down payment. Over the last several months, America's top armed service chiefs have written a series of op-eds that clearly demonstrate their competency and understanding of the challenges ahead. One can only hope America's military will have the proper funding, focus, technology and force structure to confront the access challenges it will likely face in the years to come.