【軍傳媒／軍事科技】諾斯羅普·格魯曼公司已確認，美國陸軍已訂購了 16 門最新一代 50 毫米XM913大毒蛇鏈砲 (CG)，用於在陸軍計劃中的新型作戰車輛上進行測試。該武器由該公司與皮卡汀尼兵工廠密切合作開發，除了美國陸軍將進行測試外，50毫米XM913型火砲還會提供給了通用動力陸地系統公司（GDLS）和萊茵金屬美國車輛公司安裝在兩家的XM30原型車上進行測試。
從機械結構來看，XM913 仍採用外力驅動的鏈式擊發設計，能在不依賴火藥燃氣的情況下完成供彈、閉鎖、擊發與退殼循環。這種設計在高口徑條件下尤為重要，因為 50 公釐彈藥的質量與後座能量都顯著增加，若採傳統反沖或導氣設計，對可靠性與壽命的挑戰將更為嚴苛。鏈式系統讓射擊循環更可控，也讓故障排除能以「反轉鏈條」等方式處理，這對戰場可用率而言具有實際價值。
歐洲 IFV 30/35/40 公釐潮流
過去十多年，歐洲主力步兵戰鬥車IFV火力口徑大致呈現三個主流口徑：
- 30公釐：以德國Puma的MK30-2/ABM 為代表，強調彈藥體積與攜彈量、以及空炸/可程式化彈藥在3,000公尺內的普遍效益。30公釐彈藥在攜彈量和火力之間的均衡是許多國家所能接受的。
- 35公釐：以CV90的E35（Bushmaster III 35mm）與Rheinmetall Lynx 35mm為代表，在不把彈藥尺寸推到過大過重之前，獲得更好的單發威力與對輕中裝甲的穿透/破壞能力。
- 40公釐：瑞典 CV9040（40mm Bofors L/70）這種較早期的火砲；另一條更具代表性的是英法的 40CT（40×255 伸縮彈）概念，強調「在有限砲塔空間內提高口徑與彈效」。40CT的設計目的之一，就是讓40公釐的彈藥不至於把車內空間與攜彈量壓到不可接受，同時又盡可能地提高火砲威力。
總結來看，歐洲IFV停在30/35/40公釐的火砲口徑是多數國家在IFV任務框架下做了務實取捨，網上有反裝甲飛彈提供更大的火力及射程，因為IFV的主要任務是載步兵、有可能長時間作戰、因此要有足夠攜彈量支撐持續接戰支援步兵；口徑升級帶來的單發效益，必須和攜彈量、體積重量、後勤、成本一起算。30×173的彈藥尺寸重量優勢，能讓無人砲塔攜帶更多的備射彈藥，而若改用40公釐傳統彈藥，可能面臨需頻繁離開戰鬥以補彈的壓力。
XM30選50公釐口徑火砲的意義
50公釐口徑帶來的第一個關鍵改變，就是對掩體後目標直接攻擊能力大幅提高。以XM913 50公釐的彈種設計，最具代表性的是 XM1204 HEAB-T（高爆空炸曳光彈）三種模式（觸發、延遲觸發、空炸）。其使用構想是火控電腦由感測器完成射控測距、編程彈藥引信，能在射擊後於掩體上方或穿牆後起爆，對壕溝、牆後、窗洞等遮蔽環境內人員形成有效破片殺傷，由於50公釐口徑增大穿甲能力變強，也提高對掩體的穿透能力。這種結果會改變機械化步兵排的火力分配方式，過去較常要靠迫砲、砲兵或無人機處理的躲藏在掩體後及建築殘骸間敵方步兵小隊的問題，將可由新一代IFV 50公釐主砲直接射擊解決，減少呼叫間接火力支援的延遲，同時降低對自身的威脅。
第二個改變是對敵方裝甲目標的威脅提升，50×228的APFSDS-T（如 XM1203）以穿甲彈芯提高對裝甲目標的穿透效能，能對付裝甲更厚重的裝甲車（例如加了附加裝甲的輕型車輛）、甚至在一定條件下對坦克側後方等弱點造成更大威脅。對美軍而言，不只要打得贏BMP/BTR這一代裝甲車輛，還要在未來面對同級對手新一代步戰車時，維持能有效摧毀的能力。
第三個改變，就是對把反小型無人機/反小目標的需求，以可編程50公釐機砲取代過往的.50機槍。在小型無人機普及的戰場，反無人機不可能只靠單一手段，除了基本的干擾之外，空炸彈藥能提供在特定距離內、以破片雲覆蓋來擊落無人機的選項，理論上可補足機槍對高速小目標的命中困難，同時有機會解決密集的無人機群。不過這並不等於50公釐機砲能取代專業C-UAS系統，但它會讓IFV在遭遇無人機近迫威脅時，多一個更具效果且成本低的硬殺手段，尤其是在電子干擾效果可能失效的戰場環境下。
然而50公釐口徑火砲也有他的缺點，由於彈體放大，攜彈量與持續接戰能力的壓力自然就產生。口徑增加，彈藥體積與重量幾乎必然上升。即使火砲本體長度增加有限，但是包含至退機構的更改，砲塔內空間仍會受到大幅影響，補給負擔仍會增加，而可攜彈量往往下降，這意味實際戰鬥中可能更仰賴精準射擊、補給節奏與彈種管理，狂撒彈藥的射擊方式可能已不再合適。
訓練與後勤成本上升
50 公釐單發成本、運輸、儲存、射擊場需求都更高，且可編程彈藥的訓練不只是將彈藥打出去而已，而是要把測距到彈藥編程、瞄準射擊的程序練到熟悉，這將改變現在射手的操作程序，代表訓練要大幅調整並重新熟悉，這會反映在平時訓練彈耗、射擊課目與維保體系的花費成本上。
另外50公釐空炸/延遲起爆的效益高度依賴射控系統與感測器，這意味在電子干擾、煙塵遮蔽、或車輛的感測器受損時，火力效果可能出現明顯落差。烏克蘭戰場已經證明電子戰與反電子戰的裝備拉鋸會快速演進，如果XM30的火力建立在更複雜的系統鏈上，就必須更嚴格地把「容易戰場維保、可快速替換損壞、可快速因應需求升級」納入設計哲學。
美軍XM30走向50公釐口徑機砲，反映的是美軍對未來戰場的風險評估更嚴謹，它願意用更高成本、更高系統複雜度與更重的後勤壓力，換取更強的應對能力。
總體而言，XM913「大毒蛇」並不是單純追求火力數據的產物，而是一項將工程成熟度、彈藥效能與戰場經驗整合後的結果。它象徵著美軍對步兵戰鬥車角色的重新定義：不再只是戰車與步兵之間的過渡單位，而是能在高威脅環境中，主動塑造戰場條件的核心火力平台。未來XM30搭在的50公釐XM913能否在無人機與電子戰高度動態的環境中，成功整合偵測/決策/射擊這條火控擊殺鏈做得夠快、夠可靠、夠容易升級，讓整體戰力更上一層樓。
Northrop Grumman has confirmed that the U.S. Army has ordered sixteen units of the latest-generation 50 mm XM913 Bushmaster chain gun (CG) for testing on the Army’s planned next-generation combat vehicles.
Developed through close cooperation between Northrop Grumman and Picatinny Arsenal, the 50 mm XM913 will not only undergo Army testing but will also be provided to General Dynamics Land Systems (GDLS) and Rheinmetall American Vehicles for installation on their respective XM30 prototype vehicles as part of the ongoing evaluation program.
From a mechanical perspective, the XM913 retains the externally powered chain-driven firing mechanism characteristic of the Bushmaster family. This design allows the weapon to complete feeding, chambering, firing, and extraction cycles without relying on propellant gas. Such an approach is particularly important at larger calibers, as the mass and recoil energy of 50 mm ammunition increase significantly. Conventional recoil- or gas-operated systems would face much greater challenges in terms of reliability and service life under these conditions. The chain-driven system enables tighter control of the firing cycle and allows malfunctions to be cleared through methods such as reversing the chain, providing tangible benefits in battlefield availability and maintainability.
European IFV Trends in 30, 35, and 40 mm Calibers
Over the past decade, European infantry fighting vehicles have generally converged around three main cannon calibers: 30 mm, 35 mm, and 40 mm.
The 30 mm class is represented by systems such as Germany’s Puma IFV armed with the MK30-2/ABM. This caliber emphasizes a balance between ammunition size and onboard capacity, while providing effective airburst and programmable ammunition within engagement ranges of approximately 3,000 meters. The equilibrium between carried ammunition and firepower offered by 30 mm rounds has proven acceptable to many nations.
The 35 mm class is exemplified by the CV90’s E35 (Bushmaster III 35 mm) and the 35 mm configuration offered on Rheinmetall’s Lynx IFV. This caliber seeks to deliver greater single-round lethality and improved penetration against light to medium armored targets without pushing ammunition size and weight to excessive levels.
The 40 mm category includes earlier systems such as Sweden’s CV9040 armed with the 40 mm Bofors L/70, as well as the more distinctive Anglo-French 40CT (40×255 mm cased telescoped ammunition) concept. The latter emphasizes increasing caliber and projectile effectiveness within a constrained turret volume. One of the design goals of 40CT was to prevent 40 mm ammunition from excessively reducing internal vehicle space and carried ammunition, while still maximizing firepower.
In summary, Europe’s decision to remain within the 30/35/40 mm range reflects pragmatic trade-offs made within the IFV mission framework. Anti-armor guided missiles are available to provide greater firepower and reach, while IFVs are primarily tasked with transporting infantry and sustaining prolonged combat operations. As a result, sufficient onboard ammunition capacity is essential to support continuous engagements in close cooperation with dismounted troops. Any increase in caliber must therefore be weighed against ammunition capacity, vehicle volume and weight, logistical burden, and overall cost. The size and weight advantages of 30×173 mm ammunition, for example, allow unmanned turrets to carry more ready rounds, whereas adopting conventional 40 mm ammunition can introduce pressure to disengage more frequently in order to resupply.
The Significance of the XM30’s Adoption of a 50 mm Cannon
The first major change brought by the 50 mm caliber is a substantial improvement in the ability to directly engage targets behind cover. Among the 50 mm ammunition developed for the XM913, the most representative is the XM1204 HEAB-T (High-Explosive Airburst Tracer), which offers three selectable modes: point-detonating, delayed detonation, and airburst. In operation, the fire-control computer uses sensor-derived range data to program the fuze prior to firing, enabling the projectile to detonate above cover or after penetrating walls. This allows effective fragmentation against personnel in trenches, behind walls, within window openings, or other covered positions. The increased caliber also enhances armor penetration and improves the ability to defeat structural cover.
This capability has the potential to alter fire distribution within mechanized infantry platoons. Targets such as enemy infantry squads sheltering behind cover or within building rubble—previously more often addressed by mortars, artillery, or unmanned aerial systems—could instead be directly engaged by the 50 mm main gun of next-generation IFVs. This reduces delays associated with calling for indirect fire support and lowers exposure to counterfire.
The second change is an increased threat to enemy armored targets. Using 50×228 mm APFSDS-T rounds such as the XM1203, the XM913 achieves higher penetration performance through advanced penetrator design. This allows engagement of more heavily protected armored vehicles, including light vehicles fitted with add-on armor, and under certain conditions can pose a greater threat to vulnerable areas such as the flanks or rear of main battle tanks. For the U.S. Army, the objective is not only to defeat current-generation BMP and BTR vehicles, but also to retain effective lethality against future peer IFVs.
The third change involves addressing the growing need for counter–small unmanned aerial systems and small targets by shifting from legacy .50 caliber machine guns to a programmable 50 mm cannon. In an environment where small drones are ubiquitous, counter-UAS cannot rely on a single method. In addition to electronic warfare, airburst ammunition provides an option to defeat drones within a defined engagement envelope by creating a fragmentation cloud. This may help compensate for the difficulty machine guns face when engaging fast, small targets and could potentially address dense drone threats. While this does not imply that a 50 mm cannon can replace dedicated C-UAS systems, it does give IFVs a more effective and comparatively economical hard-kill option when facing close-range drone threats, particularly in environments where electronic countermeasures may be degraded or ineffective.
Nevertheless, the 50 mm caliber also introduces clear disadvantages. Enlarged ammunition inevitably reduces carried quantities and places pressure on sustained engagement capability. As caliber increases, ammunition volume and weight rise accordingly. Even if the barrel length increase is limited, changes to recoil and feeding mechanisms significantly affect turret internal space. The logistical burden grows, and onboard ammunition capacity typically decreases. In practice, this means greater reliance on precision fire, disciplined ammunition management, and well-coordinated resupply, making indiscriminate high-volume firing increasingly impractical.
Training and logistical costs also rise. Individual 50 mm rounds are more expensive, require greater transportation and storage resources, and impose higher demands on firing ranges. Training with programmable ammunition goes beyond simply firing rounds; crews must master the full sequence from ranging and fuze programming to precise engagement. This alters existing gunnery procedures and necessitates substantial adjustments in training curricula, ammunition expenditure, and maintenance systems.
Furthermore, the effectiveness of 50 mm airburst and delayed-detonation munitions is highly dependent on the quality of fire-control systems and sensors. Under conditions of electronic interference, heavy smoke or dust, or sensor damage, firepower effectiveness may degrade significantly. The war in Ukraine has already demonstrated how rapidly electronic warfare and counter–electronic warfare capabilities evolve. If the XM30’s firepower is built upon a more complex systems chain, it must place even greater emphasis on ease of field maintenance, rapid replacement of damaged components, and the ability to quickly adapt to evolving operational requirements.
The U.S. Army’s move toward a 50 mm cannon on the XM30 reflects a more stringent assessment of future battlefield risks. It represents a willingness to accept higher costs, greater system complexity, and increased logistical burden in exchange for stronger overall combat capability.
In conclusion, the XM913 “Bushmaster” is not simply a product of firepower escalation. It represents the integration of engineering maturity, ammunition effectiveness, and lessons drawn from contemporary battlefields. It symbolizes a redefinition of the infantry fighting vehicle’s role within the U.S. Army—not merely as an intermediary between tanks and infantry, but as a core firepower platform capable of actively shaping battlefield conditions in high-threat environments. Whether the 50 mm XM913 mounted on the XM30 can successfully integrate detection, decision-making, and engagement into a fast, reliable, and upgradable kill chain under the pressures of drone-dominated and electronically contested warfare will ultimately determine whether this ambitious leap in caliber delivers its promised operational advantage.