In terms of weapons, Block 4 will eventually enable the F-35 to fire cutting edge weapons systems such as the Small Diameter Bomb II – an air-dropped bomb able to destroy targets on-the-move.

The Air Force is already working on an emerging 4th F-35 "software drop" designed to enable the stealth multi-role fighter to fire an even wider range of emerging weapons such as the new, high-tech Small Diameter Bomb II.

Following the drop of the now-operational 3F, the aircraft will incorporate new software drops in two-year increments in order to stay ahead of new threats - and service developers say a 4th software drop will be ready by 2020 or 2021.

Block 4 will include some unique partner weapons including British weapons, Turkish weapons and some of the other European country’s weapons that they want to get on their own plane, service officials explained.

(This first appeared in November 2017.)

A big part of the developmental calculus for Block 4 is to work on the kinds of enemy air defense systems and weaponry the aircraft may face from the 2020’s through the 2040’s and beyond.

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In terms of weapons, Block 4 will eventually enable the F-35 to fire cutting edge weapons systems such as the Small Diameter Bomb II – an air-dropped bomb able to destroy targets on-the-move.

While the Air Force currently uses a laser-guided bomb called the GBU-54 able to destroy moving targets, the new SDB II will be able to do this at longer ranges and in all kinds of weather conditions. In addition, the SDB II is built with a two-way, dual-band data link which enables it to change targets or adjust to different target locations while in flight.

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The Small Diameter Bomb II uses a technology called a tri-mode seeker, drawing from infrared, millimeter wave and laser-guidance. The combination of these sensors allows the weapon to track and eliminate moving targets in all kinds of weather conditions from long distances.

A tri-mode seeker provides a range of guidance and targeting options typically not used together in one system. Millimeter wave radar gives the weapon an ability to navigate through adverse weather, conditions in which other guidance systems might encounter problems reaching or pinpointing targets.

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Imaging infrared guidance allows the weapon to track and hone in on heat signatures such as the temperature of an enemy vehicle. With semi-active laser technology, the weapon can be guided to an exact point using a laser designator or laser illuminator coming from the air or the ground.

Also, the SBD II brings a new ability to track targets in flight through use of a two-way Link 16 and UHF data link, Raytheon officials said.

The millimeter wave radar turns on first. Then the data link gives it a cue and tells the seeker where to open up and look. Then, the weapon can turn on its IR (infrared) which uses heat seeking technology, Raytheon officials said.

The SBD II is engineered to weigh only 208 pounds, a lighter weight than most other air dropped bombs, so that eight of them can fit on the inside of an F-35 Joint Strike Fighter, Raytheon officials explained.

If weapons are kept in an internal weapons bay and not rested on an external weapons pod, then an aircraft can succeed in retaining its stealth properties because the shapes or contours of the weapons will not be visible to enemy radar.

About 105 pound of the SDB II is an explosive warhead which encompasses a “blast-frag” capability and a “plasma-jet” technology designed to pierce enemy armor, Raytheon officials explained.

The SDB II also has the ability to classify targets, meaning it could for example be programmed to hit only tanks in a convoy as opposed to other moving vehicles. The weapon can classify tanks, boats or wheeled targets, Raytheon developers added.

The potential value of the entire SDB II production run is expected to be $2.792 billion for 17,000 SDB II weapons – 12,000 for the Air Force and 5,000 for the Navy, Air Force officials said.

3F Software Operational

The Air Force is now in the process of operationalizing the F-35’s latest “3F” software iteration, a development which integrates additional technology and equips the stealth aircraft with a wider range of weapons such as the Small Diameter Bomb and AIM-9X, service leaders said.

After experiencing some challenges during developmental testing, the 3F software drop is now improved and sharpened up for delivery, senior Air Force officials said.

Many of the JSF’s combat capabilities are woven into the F-35s combat capabilities are woven into developmental software increments or “drops,” each designed to advance the platform’s technical abilities. There are more than 10 million individual lines of code in the JSF system.

Block 3F increases the weapons delivery capacity of the JSF as well, giving it the ability to drop a Small Diameter Bomb, 500-pound JDAM (Joint Direct Attack Munition) and AIM-9X short-range air-to-air missile, service officials explained.

The 3F software drop is preceded by earlier increments, each one bringing new technical integration to the aircraft.

Block 2B built upon the enhanced simulated weapons, datalink capabilities and early fused sensor integration of the earlier Block 2A software drop. Block 2B enables the JSF to provide basic close-air support and fire an AMRAAM (Advanced Medium Range Air-to-Air Missile), JDAM or GBU-12 (laser-guided aerial bomb), JSF program officials said.

Following Block 2B, Block 3i increased the combat capability even further, and Block 3F brings a vastly increased ability to suppress enemy air defenses.

AIM-9X

Last year, in preparation for 3F becoming operational, an Air Force  F-35 Joint Strike Fighter fired an AIM-9X Sidewinder infrared-guided air-to-air missile for the first time over a Pacific Sea Test Range, Pentagon officials said.

The F-35 took off from Edwards Air Force Base, Calif., and launched the missile at 6,000 feet, an Air Force statement said.

Designed as part of the developmental trajectory for the emerging F-35, the test-firing of the AIM-9X was intended to further the missile's ability to fire “off-boresight." This is described as an ability to target and destroy air to air targets that are not in front of the aircraft with a direct or immediate line of sight, Pentagon officials explained.

Previous test data and observers have confirmed the F-35 identified and targeted the drone with its mission systems sensors, passed the target ‘track’ information to the missile, enabled the pilot to verify targeting information using the high off-boresight capability of the helmet mounted display and launched the AIM-9X from the aircraft to engage the target drone, a statement from the Pentagon's Joint Strike Fighter Program Office said.

“If you think of a boresight in terms of a firearm… that’s the adjustments made to an optical sight, to align the barrel of a firearm with the sights.  If you think of it in aircraft terms… traditionally air-to-air missiles are fired at targets in front of the them,” Joint Strike Fighter Program Office spokesman Joe DellaVedova, previously told Scout Warrior in an interview.

The AIM-9X, he described, incorporates an agile thrust vector controlled airframe.

“For example, instead of having to position the aircraft directly in front or behind the enemy fighter… a high off-boresight weapon enables the pilot to just look to the left, right or up and down to engage a target, fire it and the missile locks on for the kill,” he explained.  

The AIM-9X is an Air Force and Navy heat-seeking infrared missile.

The AIM-9X missile, which can also be fired at surface-to-air and air-to-surface, is currently in use on a number of existing fighter aircraft such as the Air Force’s F-15E and F-16 and the Navy’s F-18 Super Hornet.

Engineered by Raytheon, the newest AIM-9X Block II weapons are built with a redesigned fuse for increased safety and a lock-on-launch capability. The missile is also configured with a data link to support what’s called “beyond visual range” engagements, meaning targets at much farther ranges picked up by sensors or early warning radar. This could provide a fighter jet with an ability to destroy enemy targets in the air while remaining at a safer stand-off distance less exposed to hostile fire.

"The AIM-9X Sidewinder is an infrared-guided, air-to-air missile employing a focal plane array sensor for unparalleled target acquisition and tracking, augmented by jet vane control technology for extreme maneuverability against a variety of high performance threats,” Mark Justus, Raytheon AIM-9X program director, told Scout Warrior in a written statement last year. "The missile also has proven capability in air-to-surface and demonstrated capability in surface-to-air missions."

Immediately prior to the test-launching of the AIM-9X, a test pilot employed an internally carried AIM-120C missile against another target drone. This target was beyond visual range and the AIM-120C was given a successful self-destruct signal right before target impact, Pentagon statements said.

The AIM-9X Block II is the current version of the AIM-9 Sidewinder short range missile family in use by more than 40 nations throughout the world, developers said.