- What PGK is: A screw‑on fuze that turns standard 155 mm shells into near‑precision rounds by adding GPS guidance and course‑correction control surfaces. It cuts delivery error and the number of rounds needed per target. jpeoaa.army.mil
- Why “GPS‑degraded” matters: Russian electronic warfare in Ukraine has blunted several GPS‑guided weapons, forcing changes in tactics and supply; Excalibur and other systems saw major performance drops. Washington Post
- New PGK hardware: The M1156A1 integrates M‑code GPS for more resilient positioning; type classification (2024) and Full Materiel Release in 2025. PEO IEWS
- Anti‑jam variant: The M1156E5 adds an anti‑jam capability for GPS‑degraded areas; Army fielding begins in 2026. PEO IEWS
- Industry push: Northrop Grumman’s PGK‑ER (Extended Range) keeps PGK’s form factor but is updated “to perform in a GPS‑degraded environment.” Northrop Grumman
- Supply chain shift: CAES is delivering 80,000 M‑code GPS antennas (2023–2026) to harden PGK against jamming. caes.com
- Scale: The Army had already taken delivery of 100,000+ PGKs by late 2022. C4ISRNet
- Design baseline: Anti‑jam was a threshold requirement in the program’s Increment II; PGK also includes a built‑in safety that prevents detonation if the predicted miss is beyond a set distance. Dote
- What’s next: LR‑PGK (XM1171/XM1172) aims to modernize the course‑correcting fuze for longer‑range guns while staying compatible with GPS upgrades. jpeoaa.army.mil
The problem: GPS guidance under fire
Wartime experience has shown that adversaries can degrade or even neutralize GPS‑guided munitions with robust electronic warfare. In 2024 reporting, Ukrainian assessments described U.S. satellite‑guided weapons losing effectiveness against Russian jamming; deliveries of some Excalibur shells reportedly halted as a result. The Washington Post
Electronic warfare analyst Thomas Withington put it plainly: “Russian RF jamming appears to have been successful in jamming these PNT signals.” European Security & Defence Reuters reached similar conclusions for GLSDB glide bombs, underscoring that the broader family of GPS‑guided weapons is vulnerable and that fixes take time. Reuters
The technical why: GPS signals arrive at Earth incredibly weak and are relatively easy to overpower with a nearby jammer; spoofing (sending false signals) is a more subtle threat. Military‑only M‑code hardens receivers with encrypted, more resilient signals—but it must actually be integrated into each weapon to matter. European Security & Defence
What PGK is—and how it behaves when GPS is shaky
PGK (M1156) replaces a standard fuze on 155 mm shells with a guidance fuze that uses GPS and small canards to trim out ballistic error. The U.S. Army’s program office describes its effect succinctly: reduced delivery error and fewer rounds per mission. jpeoaa.army.mil
Two design items are crucial in a jammed fight:
- Anti‑jam was baked into the roadmap. A 2012 operational test report lists “add anti‑jam capability” as a threshold in Increment II—well before today’s contested GPS became front‑page news. Dote
- Fail‑safe arming logic. PGK includes a selectable safety that prevents detonation if the fuze predicts a miss beyond the chosen limit—useful near friendlies or civilians, but it also means a heavily jammed round may land inert. C4ISRNet
The Army’s response: M‑code now, anti‑jam next
M1156A1 (NA37): M‑code PGK. The Army confirms the A1 variant with M‑code achieved type classification in 2024, with Full Materiel Release in 2025. As PM CAS put it, “The integration of an M‑code‑capable GPS receiver… enhances resilience against emerging threats.” PEO IEWS
M1156E5: anti‑jam PGK. The same Army update notes an E5 variant that “incorporated an anti‑jam capability” for GPS‑degraded areas, with fielding slated for 2026. PEO IEWS
These increments dovetail with the Army’s broader Assured PNT push. Project Manager PNT highlighted the cross‑portfolio effort to swap legacy GPS for M‑code and other sensors, noting, “This partnership was critical to the Army’s transition from legacy GPS to Assured PNT.” PEO IEWS
Industry’s counter‑EW move: PGK‑ER and a flooded M‑code supply chain
Northrop Grumman’s PGK‑ER keeps the existing form factor but adds technologies “to perform in a GPS‑degraded environment,” said Bernie Gruber, the company’s director of Guided Projectiles. Northrop Grumman
To make that real at scale, CAES is supplying 80,000 M‑code GPS antennas over three years under a $24 million contract—explicitly to improve anti‑jamming and security on PGK. caes.com That follows the Army already taking delivery of 100,000+ legacy PGKs by late 2022, giving the program a huge installed base to upgrade. C4ISRNet
How “GPS‑degraded” changes fire missions
- More resilient signals: M‑code reception and anti‑jam signal processing aim to keep PGK guiding where earlier receivers lost lock. (The Army says the A1’s M‑code “dramatically increases” accuracy in complex terrain and weather.) PEO IEWS
- Safety vs. lethality trade‑offs: PGK’s fail‑safe helps prevent unintended effects but can reduce effects under severe jamming—hence the push to strengthen the navigation link. C4ISRNet
- Doctrine and networks: Assured PNT upgrades (MAPS/DAPS, anti‑jam antennas, software hardening) across the force improve the whole kill chain’s timing and targeting in jammed zones, benefiting artillery fire control—PGK included. PEO IEWS
How PGK stacks up against alternatives in a jammed fight
- Excalibur vs. PGK: Excalibur offers exquisite accuracy, but Ukraine showed GPS jamming can crater effects; PGK gives cheaper near‑precision at scale with the Army now hardening it via M‑code/anti‑jam. The Washington Post
- Glide and rocket munitions: GLSDB and some JDAM‑ER uses were impeded by Russian jamming; one response is adding home‑on‑jam seekers to some air‑delivered weapons. (There’s no public evidence of HOJ on PGK.) Reuters
- Long‑range guns: LR‑PGK is being developed to keep course‑correcting fuzes viable as cannon ranges grow (ERCA/58‑caliber, XM1113), with explicit compatibility for GPS upgrades. jpeoaa.army.mil
Expert voices (short quotes)
- Bernie Gruber, Northrop Grumman: “We’ve updated and added technologies to perform in a GPS‑degraded environment.” Northrop Grumman
- Mike Trzeciak, PM PNT: “This partnership was critical to the Army’s transition from legacy GPS to Assured PNT.” PEO IEWS
- Col. Leon L. Rogers II, PM CAS (on A1): “Integrating an M‑code‑capable GPS receiver… enhances resilience against emerging threats.” PEO IEWS
- DOT&E (2012) on PGK’s roadmap: “Improve delivery accuracy… and add anti‑jam capability.” Dote
- Thomas Withington, ESD: “Russian RF jamming appears to have been successful.” European Security & Defence
- C4ISRNET (on safety feature): PGK includes a selectable feature that “prevents detonation” if the predicted miss exceeds the set limit. C4ISRNet
Outlook: What to watch through 2026
- A1 fielding across units. 2025 FMR enables wider M‑code rollout to artillery formations; watch for reported increases in “first‑round effects” under EW. PEO IEWS
- E5 anti‑jam introduction (2026). Expect user feedback on how the new variant holds lock under field jamming and whether fail‑safe non‑detonations decline accordingly. PEO IEWS
- PGK‑ER and LR‑PGK maturation. As ranges stretch and threats evolve, extended‑range and long‑range fuze kits that are GPS‑upgrade‑ready will be the baton pass from today’s fixes to tomorrow’s doctrines. Northrop Grumman
- Assured‑PNT at scale. The Army cites tens of thousands of M‑code receivers delivered and thousands of assured‑PNT systems fielded in FY2024 alone—momentum that underwrites PGK’s resilience. PEO IEWS
Sources & further reading
- Official program pages: JPEO A&A on PGK and Long Range PGK; Army PEO IEW&S on Assured PNT partnerships, A1 FMR 2025, and E5 anti‑jam fielding. jpeoaa.army.mil
- Industry updates: Northrop on PGK‑ER and modernization; CAES on M‑code GPS antenna deliveries. Northrop Grumman
- Operational context: Washington Post, Business Insider, Reuters, and European Security & Defence coverage of GPS jamming in Ukraine and its impact on precision weapons. European Security
- Background & test history: DOT&E PGK annual report; C4ISRNET on the 100,000‑kit milestone and PGK’s safety feature. Dote
Bottom line: PGK’s value proposition—make every round count—survives in a GPS‑degraded world only if its navigation link survives. That’s exactly what A1 (M‑code), E5 (anti‑jam), and PGK‑ER are built to do, with the Army’s Assured‑PNT enterprise pushing the whole kill chain in the same direction. PEO IEWS
